Bug 1359556 - Optimize cloneNode by preinitializing attribute and child arrays r=bz

Currently, attribute and child arrays (implemented in dom/base/nsAttrAndChildArray.h) start out empty. When cloning, the array ends up being resized multiple times in order to add the attributes and children that are being cloned from the original node. This would be quicker if the array was initialized to the correct size in the first place so that resizes are not necessary.

However, preallocating space for children is only necessary when performing a deep clone. Therefore, an additional parameter is being added to the Clone, CopyInnerTo, and CloneDocHelper methods to indicate whether preallocation of children should happen. Attributes are copied either way, so that part of the array is preallocated in both cases.

MozReview-Commit-ID: 3iVezeAKXnI

--HG--
extra : rebase_source : 9c3deec6d7aafd6411044d623d4863637b45fd58

dom/base/Attr.cpp

@@ -251,7 +251,8 @@ Attr::SetNodeValueInternal(const nsAString& aNodeValue, ErrorResult& aError)
 }
 
 nsresult
-Attr::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
+Attr::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+            bool aPreallocateChildren) const
 {
   nsAutoString value;
   const_cast<Attr*>(this)->GetValue(value);

dom/base/Attr.h

@@ -70,7 +70,8 @@ public:
   virtual nsresult InsertChildAt(nsIContent* aKid, uint32_t aIndex,
                                  bool aNotify) override;
   virtual void RemoveChildAt(uint32_t aIndex, bool aNotify) override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
   virtual already_AddRefed<nsIURI> GetBaseURI(bool aTryUseXHRDocBaseURI = false) const override;
 
   static void Initialize();

dom/base/DocumentFragment.h

@@ -144,7 +144,8 @@ protected:
   {
   }
 
-  nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                 bool aPreallocateChildren) const override;
   nsIContent* mHost; // Weak
 };
 

dom/base/Element.h

@@ -1653,7 +1653,8 @@ inline void nsINode::UnsetRestyleFlagsIfGecko()
  */
 #define NS_IMPL_ELEMENT_CLONE(_elementName)                                 \
 nsresult                                                                    \
-_elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const \
+_elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,   \
+                    bool aPreallocateChildren) const                        \
 {                                                                           \
   *aResult = nullptr;                                                       \
   already_AddRefed<mozilla::dom::NodeInfo> ni =                             \
@@ -1664,7 +1665,7 @@ _elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
   }                                                                         \
                                                                             \
   nsCOMPtr<nsINode> kungFuDeathGrip = it;                                   \
-  nsresult rv = const_cast<_elementName*>(this)->CopyInnerTo(it);           \
+  nsresult rv = const_cast<_elementName*>(this)->CopyInnerTo(it, aPreallocateChildren); \
   if (NS_SUCCEEDED(rv)) {                                                   \
     kungFuDeathGrip.swap(*aResult);                                         \
   }                                                                         \
@@ -1674,7 +1675,8 @@ _elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
 
 #define NS_IMPL_ELEMENT_CLONE_WITH_INIT(_elementName)                       \
 nsresult                                                                    \
-_elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const \
+_elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,   \
+                    bool aPreallocateChildren) const                        \
 {                                                                           \
   *aResult = nullptr;                                                       \
   already_AddRefed<mozilla::dom::NodeInfo> ni =                             \
@@ -1686,7 +1688,7 @@ _elementName::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
                                                                             \
   nsCOMPtr<nsINode> kungFuDeathGrip = it;                                   \
   nsresult rv = it->Init();                                                 \
-  nsresult rv2 = const_cast<_elementName*>(this)->CopyInnerTo(it);          \
+  nsresult rv2 = const_cast<_elementName*>(this)->CopyInnerTo(it, aPreallocateChildren); \
   if (NS_FAILED(rv2)) {                                                     \
     rv = rv2;                                                               \
   }                                                                         \

dom/base/FragmentOrElement.cpp

@@ -2058,15 +2058,20 @@ NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE(FragmentOrElement,
 //----------------------------------------------------------------------
 
 nsresult
-FragmentOrElement::CopyInnerTo(FragmentOrElement* aDst)
+FragmentOrElement::CopyInnerTo(FragmentOrElement* aDst,
+                               bool aPreallocateChildren)
 {
+  nsresult rv = aDst->mAttrsAndChildren.EnsureCapacityToClone(mAttrsAndChildren,
+                                                              aPreallocateChildren);
+  NS_ENSURE_SUCCESS(rv, rv);
+
   uint32_t i, count = mAttrsAndChildren.AttrCount();
   for (i = 0; i < count; ++i) {
     const nsAttrName* name = mAttrsAndChildren.AttrNameAt(i);
     const nsAttrValue* value = mAttrsAndChildren.AttrAt(i);
     nsAutoString valStr;
     value->ToString(valStr);
-    nsresult rv = aDst->SetAttr(name->NamespaceID(), name->LocalName(),
+    rv = aDst->SetAttr(name->NamespaceID(), name->LocalName(),
                                 name->GetPrefix(), valStr, false);
     NS_ENSURE_SUCCESS(rv, rv);
   }

dom/base/FragmentOrElement.h

@@ -236,7 +236,7 @@ protected:
    * Copy attributes and state to another element
    * @param aDest the object to copy to
    */
-  nsresult CopyInnerTo(FragmentOrElement* aDest);
+  nsresult CopyInnerTo(FragmentOrElement* aDest, bool aPreallocateChildren);
 
 public:
   // Because of a bug in MS C++ compiler nsDOMSlots must be declared public,

dom/base/ShadowRoot.cpp

@@ -710,7 +710,8 @@ ShadowRoot::ContentRemoved(nsIDocument* aDocument,
 }
 
 nsresult
-ShadowRoot::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
+ShadowRoot::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                  bool aPreallocateChildren) const
 {
   *aResult = nullptr;
   return NS_ERROR_DOM_DATA_CLONE_ERR;

dom/base/ShadowRoot.h

@@ -186,7 +186,8 @@ protected:
   // so instead we track it here.
   bool mIsComposedDocParticipant;
 
-  nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                 bool aPreallocateChildren) const override;
 };
 
 class ShadowRootStyleSheetList : public StyleSheetList

dom/base/nsAttrAndChildArray.cpp

@@ -794,6 +794,44 @@ nsAttrAndChildArray::GetMapped() const
   return mImpl ? mImpl->mMappedAttrs : nullptr;
 }
 
+nsresult nsAttrAndChildArray::EnsureCapacityToClone(const nsAttrAndChildArray& aOther,
+                                                    bool aAllocateChildren)
+{
+  NS_PRECONDITION(!mImpl, "nsAttrAndChildArray::EnsureCapacityToClone requires the array be empty when called");
+
+  uint32_t attrCount = aOther.NonMappedAttrCount();
+  uint32_t childCount = 0;
+  if (aAllocateChildren) {
+    childCount = aOther.ChildCount();
+  }
+
+  if (attrCount == 0 && childCount == 0) {
+    return NS_OK;
+  }
+
+  // No need to use a CheckedUint32 because we are cloning. We know that we
+  // have already allocated an nsAttrAndChildArray of this size.
+  uint32_t size = attrCount;
+  size *= ATTRSIZE;
+  size += childCount;
+  uint32_t totalSize = size;
+  totalSize += NS_IMPL_EXTRA_SIZE;
+
+  mImpl = static_cast<Impl*>(malloc(totalSize * sizeof(void*)));
+  NS_ENSURE_TRUE(mImpl, NS_ERROR_OUT_OF_MEMORY);
+
+  mImpl->mMappedAttrs = nullptr;
+  mImpl->mBufferSize = size;
+
+  // The array is now the right size, but we should reserve the correct
+  // number of slots for attributes so that children don't get written into
+  // that part of the array (which will then need to be moved later).
+  memset(static_cast<void*>(mImpl->mBuffer), 0, sizeof(InternalAttr) * attrCount);
+  SetAttrSlotAndChildCount(attrCount, 0);
+
+  return NS_OK;
+}
+
 bool
 nsAttrAndChildArray::GrowBy(uint32_t aGrowSize)
 {

dom/base/nsAttrAndChildArray.h

@@ -143,6 +143,13 @@ public:
   // Will assert off main thread
   void ClearMappedServoStyle();
 
+  // Increases capacity (if necessary) to have enough space to accomodate the
+  // unmapped attributes and children of |aOther|. If |aAllocateChildren| is not
+  // true, only enough space for unmapped attributes will be reserved.
+  // It is REQUIRED that this function be called ONLY when the array is empty.
+  nsresult EnsureCapacityToClone(const nsAttrAndChildArray& aOther,
+                                 bool aAllocateChildren);
+
 private:
   nsAttrAndChildArray(const nsAttrAndChildArray& aOther) = delete;
   nsAttrAndChildArray& operator=(const nsAttrAndChildArray& aOther) = delete;

dom/base/nsDocument.cpp

@@ -9318,7 +9318,7 @@ nsDocument::RefreshLinkHrefs()
 }
 
 nsresult
-nsDocument::CloneDocHelper(nsDocument* clone) const
+nsDocument::CloneDocHelper(nsDocument* clone, bool aPreallocateChildren) const
 {
   clone->mIsStaticDocument = mCreatingStaticClone;
 
@@ -9395,6 +9395,11 @@ nsDocument::CloneDocHelper(nsDocument* clone) const
   clone->mType = mType;
   clone->mXMLDeclarationBits = mXMLDeclarationBits;
   clone->mBaseTarget = mBaseTarget;
+
+  // Preallocate attributes and child arrays
+  rv = clone->mChildren.EnsureCapacityToClone(mChildren, aPreallocateChildren);
+  NS_ENSURE_SUCCESS(rv, rv);
+
   return NS_OK;
 }
 

dom/base/nsDocument.h

@@ -812,7 +812,8 @@ public:
   virtual nsresult InsertChildAt(nsIContent* aKid, uint32_t aIndex,
                                  bool aNotify) override;
   virtual void RemoveChildAt(uint32_t aIndex, bool aNotify) override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override
   {
     return NS_ERROR_NOT_IMPLEMENTED;
   }
@@ -1011,7 +1012,7 @@ public:
     mLoadedAsInteractiveData = aLoadedAsInteractiveData;
   }
 
-  nsresult CloneDocHelper(nsDocument* clone) const;
+  nsresult CloneDocHelper(nsDocument* clone, bool aPreallocateChildren) const;
 
   void MaybeInitializeFinalizeFrameLoaders();
 

dom/base/nsGenericDOMDataNode.h

@@ -167,7 +167,8 @@ public:
   virtual nsChangeHint GetAttributeChangeHint(const nsIAtom* aAttribute,
                                               int32_t aModType) const;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override
   {
     nsCOMPtr<nsINode> result = CloneDataNode(aNodeInfo, true);
     result.forget(aResult);

dom/base/nsINode.h

@@ -1084,8 +1084,11 @@ public:
    *
    * @param aNodeInfo the nodeinfo to use for the clone
    * @param aResult the clone
+   * @param aPreallocateChildren If true, the array of children will be
+   *                             preallocated in preparation for a deep copy.
    */
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const = 0;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const = 0;
 
   // This class can be extended by subclasses that wish to store more
   // information in the slots.

dom/base/nsNodeUtils.cpp

@@ -473,7 +473,7 @@ nsNodeUtils::CloneAndAdopt(nsINode *aNode, bool aClone, bool aDeep,
 
   nsCOMPtr<nsINode> clone;
   if (aClone) {
-    rv = aNode->Clone(nodeInfo, getter_AddRefs(clone));
+    rv = aNode->Clone(nodeInfo, getter_AddRefs(clone), aDeep);
     NS_ENSURE_SUCCESS(rv, rv);
 
     if (clone->IsElement()) {

dom/html/HTMLAnchorElement.h

@@ -81,7 +81,8 @@ public:
                                 const nsAString& aValue,
                                 nsAttrValue& aResult) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual EventStates IntrinsicState() const override;
 

dom/html/HTMLAreaElement.h

@@ -67,7 +67,8 @@ public:
   virtual nsresult UnsetAttr(int32_t aNameSpaceID, nsIAtom* aAttribute,
                              bool aNotify) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual EventStates IntrinsicState() const override;
 

dom/html/HTMLAudioElement.h

@@ -29,7 +29,8 @@ public:
   // nsIDOMHTMLMediaElement
   using HTMLMediaElement::GetPaused;
 
-  virtual nsresult Clone(NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
   virtual nsresult SetAcceptHeader(nsIHttpChannel* aChannel) override;
 
   virtual nsIDOMNode* AsDOMNode() override { return this; }

dom/html/HTMLBRElement.h

@@ -25,7 +25,8 @@ public:
                                 nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   bool Clear()
   {

dom/html/HTMLBodyElement.h

@@ -106,7 +106,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual already_AddRefed<nsIEditor> GetAssociatedEditor() override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual bool IsEventAttributeName(nsIAtom* aName) override;
 

dom/html/HTMLButtonElement.h

@@ -62,7 +62,8 @@ public:
                      EventChainPostVisitor& aVisitor) override;
 
   // nsINode
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
   virtual JSObject* WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 
   // nsIContent

dom/html/HTMLCanvasElement.cpp

@@ -561,9 +561,10 @@ HTMLCanvasElement::GetOriginalCanvas()
 }
 
 nsresult
-HTMLCanvasElement::CopyInnerTo(Element* aDest)
+HTMLCanvasElement::CopyInnerTo(Element* aDest,
+                               bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
   if (aDest->OwnerDoc()->IsStaticDocument()) {
     HTMLCanvasElement* dest = static_cast<HTMLCanvasElement*>(aDest);

dom/html/HTMLCanvasElement.h

@@ -307,8 +307,10 @@ public:
   virtual nsresult UnsetAttr(int32_t aNameSpaceID, nsIAtom* aName,
                              bool aNotify) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
-  nsresult CopyInnerTo(mozilla::dom::Element* aDest);
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
+  nsresult CopyInnerTo(mozilla::dom::Element* aDest,
+                       bool aPreallocateChildren);
 
   virtual nsresult GetEventTargetParent(
                      mozilla::EventChainPreVisitor& aVisitor) override;

dom/html/HTMLContentElement.h

@@ -40,7 +40,8 @@ public:
 
   virtual bool IsHTMLContentElement() const override { return true; }
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual nsIDOMNode* AsDOMNode() override { return this; }
 

dom/html/HTMLDataElement.h

@@ -31,7 +31,8 @@ public:
     SetHTMLAttr(nsGkAtoms::value, aValue, aError);
   }
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLDataElement();

dom/html/HTMLDataListElement.h

@@ -34,7 +34,8 @@ public:
   }
 
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // This function is used to generate the nsContentList (option elements).
   static bool MatchOptions(Element* aElement, int32_t aNamespaceID,

dom/html/HTMLDetailsElement.h

@@ -32,7 +32,8 @@ public:
 
   nsIContent* GetFirstSummary() const;
 
-  nsresult Clone(NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  nsresult Clone(NodeInfo* aNodeInfo, nsINode** aResult,
+                 bool aPreallocateChildren) const override;
 
   nsChangeHint GetAttributeChangeHint(const nsIAtom* aAttribute,
                                       int32_t aModType) const override;

dom/html/HTMLDialogElement.h

@@ -24,7 +24,8 @@ public:
 
   NS_IMPL_FROMCONTENT_HTML_WITH_TAG(HTMLDialogElement, dialog)
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   static bool IsDialogEnabled();
 

dom/html/HTMLDivElement.h

@@ -35,7 +35,8 @@ public:
                               nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLDivElement();

dom/html/HTMLElement.cpp

@@ -18,7 +18,8 @@ public:
   virtual ~HTMLElement();
 
   virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo,
-                         nsINode** aResult) const override;
+                         nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual JSObject* WrapNode(JSContext *aCx, JS::Handle<JSObject*> aGivenProto) override;

dom/html/HTMLFieldSetElement.h

@@ -53,7 +53,8 @@ public:
   NS_IMETHOD Reset() override;
   NS_IMETHOD SubmitNamesValues(HTMLFormSubmission* aFormSubmission) override;
   virtual bool IsDisabledForEvents(EventMessage aMessage) override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   const nsIContent* GetFirstLegend() const { return mFirstLegend; }
 

dom/html/HTMLFontElement.h

@@ -51,7 +51,8 @@ public:
                                 nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLFontElement();

dom/html/HTMLFormElement.h

@@ -122,7 +122,8 @@ public:
    */
   void ForgetCurrentSubmission();
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLFormElement,
                                            nsGenericHTMLElement)

dom/html/HTMLFrameElement.h

@@ -35,7 +35,8 @@ public:
                               nsIAtom* aAttribute,
                               const nsAString& aValue,
                               nsAttrValue& aResult) override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // WebIDL API
   // The XPCOM GetFrameBorder is OK for us

dom/html/HTMLFrameSetElement.h

@@ -136,7 +136,8 @@ public:
   virtual nsChangeHint GetAttributeChangeHint(const nsIAtom* aAttribute,
                                               int32_t aModType) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLFrameSetElement();

dom/html/HTMLHRElement.h

@@ -35,7 +35,8 @@ public:
                               nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // WebIDL API
   void SetAlign(const nsAString& aAlign, ErrorResult& aError)

dom/html/HTMLHeadingElement.h

@@ -27,7 +27,8 @@ public:
                               nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   void SetAlign(const nsAString& aAlign, ErrorResult& aError)
   {

dom/html/HTMLIFrameElement.h

@@ -44,7 +44,8 @@ public:
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   nsresult SetAttr(int32_t aNameSpaceID, nsIAtom* aName,
                    const nsAString& aValue, bool aNotify)

dom/html/HTMLImageElement.cpp

@@ -810,7 +810,7 @@ HTMLImageElement::GetNaturalWidth(uint32_t* aNaturalWidth)
 }
 
 nsresult
-HTMLImageElement::CopyInnerTo(Element* aDest)
+HTMLImageElement::CopyInnerTo(Element* aDest, bool aPreallocateChildren)
 {
   bool destIsStatic = aDest->OwnerDoc()->IsStaticDocument();
   auto dest = static_cast<HTMLImageElement*>(aDest);
@@ -818,7 +818,7 @@ HTMLImageElement::CopyInnerTo(Element* aDest)
     CreateStaticImageClone(dest);
   }
 
-  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest, aPreallocateChildren);
   if (NS_FAILED(rv)) {
     return rv;
   }

dom/html/HTMLImageElement.h

@@ -92,11 +92,12 @@ public:
   virtual void UnbindFromTree(bool aDeep, bool aNullParent) override;
 
   virtual EventStates IntrinsicState() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual void NodeInfoChanged(nsIDocument* aOldDoc) override;
 
-  nsresult CopyInnerTo(Element* aDest);
+  nsresult CopyInnerTo(Element* aDest, bool aPreallocateChildren);
 
   void MaybeLoadImage();
 

dom/html/HTMLInputElement.cpp

@@ -1285,7 +1285,8 @@ NS_IMPL_NSICONSTRAINTVALIDATION_EXCEPT_SETCUSTOMVALIDITY(HTMLInputElement)
 // nsIDOMNode
 
 nsresult
-HTMLInputElement::Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const
+HTMLInputElement::Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                        bool aPreallocateArrays) const
 {
   *aResult = nullptr;
 
@@ -1293,7 +1294,7 @@ HTMLInputElement::Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) co
   RefPtr<HTMLInputElement> it = new HTMLInputElement(ni, NOT_FROM_PARSER,
                                                      FromClone::yes);
 
-  nsresult rv = const_cast<HTMLInputElement*>(this)->CopyInnerTo(it);
+  nsresult rv = const_cast<HTMLInputElement*>(this)->CopyInnerTo(it, aPreallocateArrays);
   NS_ENSURE_SUCCESS(rv, rv);
 
   switch (GetValueMode()) {

dom/html/HTMLInputElement.h

@@ -285,7 +285,8 @@ public:
    */
   already_AddRefed<nsIDOMHTMLInputElement> GetSelectedRadioButton() const;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLInputElement,
                                            nsGenericHTMLFormElementWithState)

dom/html/HTMLLIElement.h

@@ -36,7 +36,8 @@ public:
                                 nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // WebIDL API
   void GetType(DOMString& aType)

dom/html/HTMLLabelElement.h

@@ -66,7 +66,8 @@ public:
                      EventChainPostVisitor& aVisitor) override;
   virtual bool PerformAccesskey(bool aKeyCausesActivation,
                                 bool aIsTrustedEvent) override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   nsGenericHTMLElement* GetLabeledElement() const;
 protected:

dom/html/HTMLLegendElement.h

@@ -53,7 +53,8 @@ public:
   virtual nsresult UnsetAttr(int32_t aNameSpaceID, nsIAtom* aAttribute,
                              bool aNotify) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   Element* GetFormElement() const
   {

dom/html/HTMLLinkElement.h

@@ -52,7 +52,8 @@ public:
                      EventChainPostVisitor& aVisitor) override;
 
   // nsINode
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
   virtual JSObject* WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 
   // nsIContent

dom/html/HTMLMapElement.h

@@ -29,7 +29,8 @@ public:
   // nsIDOMHTMLMapElement
   NS_DECL_NSIDOMHTMLMAPELEMENT
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_NO_UNLINK(HTMLMapElement,
                                                      nsGenericHTMLElement)

dom/html/HTMLMediaElement.cpp

@@ -6376,9 +6376,9 @@ already_AddRefed<nsILoadGroup> HTMLMediaElement::GetDocumentLoadGroup()
 }
 
 nsresult
-HTMLMediaElement::CopyInnerTo(Element* aDest)
+HTMLMediaElement::CopyInnerTo(Element* aDest, bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
   if (aDest->OwnerDoc()->IsStaticDocument()) {
     HTMLMediaElement* dest = static_cast<HTMLMediaElement*>(aDest);

dom/html/HTMLMediaElement.h

@@ -385,7 +385,7 @@ public:
    */
   bool GetPlayedOrSeeked() const { return mHasPlayedOrSeeked; }
 
-  nsresult CopyInnerTo(Element* aDest);
+  nsresult CopyInnerTo(Element* aDest, bool aPreallocateChildren);
 
   /**
    * Sets the Accept header on the HTTP channel to the required

dom/html/HTMLMenuElement.h

@@ -37,7 +37,8 @@ public:
                                 const nsAString& aValue,
                                 nsAttrValue& aResult) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   uint8_t GetType() const { return mType; }
 

dom/html/HTMLMenuItemElement.cpp

@@ -178,13 +178,14 @@ NS_IMPL_ISUPPORTS_INHERITED(HTMLMenuItemElement, nsGenericHTMLElement,
 
 //NS_IMPL_ELEMENT_CLONE(HTMLMenuItemElement)
 nsresult
-HTMLMenuItemElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
+HTMLMenuItemElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                           bool aPreallocateArrays) const
 {
   *aResult = nullptr;
   already_AddRefed<mozilla::dom::NodeInfo> ni = RefPtr<mozilla::dom::NodeInfo>(aNodeInfo).forget();
   RefPtr<HTMLMenuItemElement> it =
     new HTMLMenuItemElement(ni, NOT_FROM_PARSER);
-  nsresult rv = const_cast<HTMLMenuItemElement*>(this)->CopyInnerTo(it);
+  nsresult rv = const_cast<HTMLMenuItemElement*>(this)->CopyInnerTo(it, aPreallocateArrays);
   if (NS_SUCCEEDED(rv)) {
     switch (mType) {
       case CMD_TYPE_CHECKBOX:

dom/html/HTMLMenuItemElement.h

@@ -52,7 +52,8 @@ public:
 
   virtual void DoneCreatingElement() override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   uint8_t GetType() const { return mType; }
 

dom/html/HTMLMetaElement.h

@@ -37,7 +37,8 @@ public:
 
   void CreateAndDispatchEvent(nsIDocument* aDoc, const nsAString& aEventName);
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // XPCOM GetName is fine.
   void SetName(const nsAString& aName, ErrorResult& aRv)

dom/html/HTMLMeterElement.h

@@ -24,7 +24,8 @@ public:
 
   virtual EventStates IntrinsicState() const override;
 
-  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                 bool aPreallocateChildren) const override;
 
   bool ParseAttribute(int32_t aNamespaceID, nsIAtom* aAttribute,
                       const nsAString& aValue, nsAttrValue& aResult) override;

dom/html/HTMLModElement.h

@@ -19,7 +19,8 @@ class HTMLModElement final : public nsGenericHTMLElement
 public:
   explicit HTMLModElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo);
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   void GetCite(nsString& aCite)
   {

dom/html/HTMLObjectElement.cpp

@@ -570,9 +570,10 @@ HTMLObjectElement::DestroyContent()
 }
 
 nsresult
-HTMLObjectElement::CopyInnerTo(Element* aDest)
+HTMLObjectElement::CopyInnerTo(Element* aDest, bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLFormElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLFormElement::CopyInnerTo(aDest,
+                                                      aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   if (aDest->OwnerDoc()->IsStaticDocument()) {

dom/html/HTMLObjectElement.h

@@ -89,9 +89,10 @@ public:
   // nsObjectLoadingContent
   virtual uint32_t GetCapabilities() const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
-  nsresult CopyInnerTo(Element* aDest);
+  nsresult CopyInnerTo(Element* aDest, bool aPreallocateChildren);
 
   void StartObjectLoad() { StartObjectLoad(true, false); }
 

dom/html/HTMLOptGroupElement.h

@@ -40,7 +40,8 @@ public:
 
   virtual EventStates IntrinsicState() const override;
  
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual nsresult AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
                                 const nsAttrValue* aValue, bool aNotify) override;

dom/html/HTMLOptionElement.cpp

@@ -437,9 +437,9 @@ HTMLOptionElement::Option(const GlobalObject& aGlobal,
 }
 
 nsresult
-HTMLOptionElement::CopyInnerTo(Element* aDest)
+HTMLOptionElement::CopyInnerTo(Element* aDest, bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   if (aDest->OwnerDoc()->IsStaticDocument()) {

dom/html/HTMLOptionElement.h

@@ -63,9 +63,10 @@ public:
   // nsIContent
   virtual EventStates IntrinsicState() const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
-  nsresult CopyInnerTo(mozilla::dom::Element* aDest);
+  nsresult CopyInnerTo(mozilla::dom::Element* aDest, bool aPreallocateChildren);
 
   virtual bool IsDisabled() const override {
     return HasAttr(kNameSpaceID_None, nsGkAtoms::disabled);

dom/html/HTMLOutputElement.h

@@ -36,7 +36,8 @@ public:
 
   virtual bool IsDisabled() const override { return false; }
 
-  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                 bool aPreallocateChildren) const override;
 
   bool ParseAttribute(int32_t aNamespaceID, nsIAtom* aAttribute,
                         const nsAString& aValue, nsAttrValue& aResult) override;

dom/html/HTMLParagraphElement.h

@@ -37,7 +37,8 @@ public:
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // WebIDL API
   // The XPCOM GetAlign is fine for our purposes

dom/html/HTMLPictureElement.h

@@ -26,7 +26,8 @@ public:
   // nsIDOMHTMLPictureElement
   NS_DECL_NSIDOMHTMLPICTUREELEMENT
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
   virtual void RemoveChildAt(uint32_t aIndex, bool aNotify) override;
   virtual nsresult InsertChildAt(nsIContent* aKid, uint32_t aIndex, bool aNotify) override;
 

dom/html/HTMLPreElement.h

@@ -38,7 +38,8 @@ public:
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // WebIDL API
   int32_t Width() const

dom/html/HTMLProgressElement.h

@@ -23,7 +23,8 @@ public:
 
   EventStates IntrinsicState() const override;
 
-  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                 bool aPreallocateChildren) const override;
 
   bool ParseAttribute(int32_t aNamespaceID, nsIAtom* aAttribute,
                         const nsAString& aValue, nsAttrValue& aResult) override;

dom/html/HTMLScriptElement.cpp

@@ -93,7 +93,8 @@ HTMLScriptElement::ParseAttribute(int32_t aNamespaceID,
 }
 
 nsresult
-HTMLScriptElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
+HTMLScriptElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const
 {
   *aResult = nullptr;
 
@@ -101,7 +102,7 @@ HTMLScriptElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) c
   HTMLScriptElement* it = new HTMLScriptElement(ni, NOT_FROM_PARSER);
 
   nsCOMPtr<nsINode> kungFuDeathGrip = it;
-  nsresult rv = const_cast<HTMLScriptElement*>(this)->CopyInnerTo(it);
+  nsresult rv = const_cast<HTMLScriptElement*>(this)->CopyInnerTo(it, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   // The clone should be marked evaluated if we are.

dom/html/HTMLScriptElement.h

@@ -53,7 +53,8 @@ public:
                               const nsAString& aValue,
                               nsAttrValue& aResult) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // Element
   virtual nsresult AfterSetAttr(int32_t aNamespaceID, nsIAtom* aName,

dom/html/HTMLSelectElement.h

@@ -402,7 +402,8 @@ public:
                                               int32_t aModType) const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLSelectElement,
                                            nsGenericHTMLFormElementWithState)

dom/html/HTMLShadowElement.h

@@ -39,7 +39,8 @@ public:
 
   virtual bool IsHTMLShadowElement() const override { return true; }
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual nsresult BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                               nsIContent* aBindingParent,

dom/html/HTMLSharedElement.h

@@ -81,7 +81,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // WebIDL API
   // HTMLParamElement

dom/html/HTMLSharedListElement.h

@@ -41,7 +41,8 @@ public:
                                 nsAttrValue& aResult) override;
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   bool Reversed() const
   {

dom/html/HTMLSharedObjectElement.cpp

@@ -346,9 +346,9 @@ HTMLSharedObjectElement::DestroyContent()
 }
 
 nsresult
-HTMLSharedObjectElement::CopyInnerTo(Element* aDest)
+HTMLSharedObjectElement::CopyInnerTo(Element* aDest, bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   if (aDest->OwnerDoc()->IsStaticDocument()) {

dom/html/HTMLSharedObjectElement.h

@@ -79,9 +79,10 @@ public:
   // nsObjectLoadingContent
   virtual uint32_t GetCapabilities() const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
-  nsresult CopyInnerTo(Element* aDest);
+  nsresult CopyInnerTo(Element* aDest, bool aPreallocateChildren);
 
   void StartObjectLoad() { StartObjectLoad(true, false); }
 

dom/html/HTMLSourceElement.h

@@ -35,7 +35,8 @@ public:
   // nsIDOMHTMLSourceElement
   NS_DECL_NSIDOMHTMLSOURCEELEMENT
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   // Override BindToTree() so that we can trigger a load when we add a
   // child source element.

dom/html/HTMLSpanElement.h

@@ -26,7 +26,8 @@ public:
   {
   }
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLSpanElement();

dom/html/HTMLStyleElement.h

@@ -50,7 +50,8 @@ public:
                                 const nsAttrValue* aValue,
                                 bool aNotify) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // nsIMutationObserver
   NS_DECL_NSIMUTATIONOBSERVER_CHARACTERDATACHANGED

dom/html/HTMLSummaryElement.h

@@ -29,7 +29,8 @@ public:
 
   NS_IMPL_FROMCONTENT_HTML_WITH_TAG(HTMLSummaryElement, summary)
 
-  nsresult Clone(NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  nsresult Clone(NodeInfo* aNodeInfo, nsINode** aResult,
+                 bool aPreallocateChildren) const override;
 
   nsresult PostHandleEvent(EventChainPostVisitor& aVisitor) override;
 

dom/html/HTMLTableCaptionElement.h

@@ -37,7 +37,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLTableCaptionElement();

dom/html/HTMLTableCellElement.h

@@ -151,7 +151,8 @@ public:
   // Get mapped attributes of ancestor table, if any
   nsMappedAttributes* GetMappedAttributesInheritedFromTable() const;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLTableCellElement();

dom/html/HTMLTableColElement.h

@@ -79,7 +79,8 @@ public:
   nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLTableColElement();

dom/html/HTMLTableElement.h

@@ -189,7 +189,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual nsresult BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                               nsIContent* aBindingParent,

dom/html/HTMLTableRowElement.h

@@ -85,7 +85,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_NO_UNLINK(HTMLTableRowElement,
                                                      nsGenericHTMLElement)

dom/html/HTMLTableSectionElement.h

@@ -70,7 +70,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_NO_UNLINK(HTMLTableSectionElement,
                                                      nsGenericHTMLElement)

dom/html/HTMLTemplateElement.h

@@ -26,7 +26,8 @@ public:
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLTemplateElement,
                                            nsGenericHTMLElement)
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   DocumentFragment* Content()
   {

dom/html/HTMLTextAreaElement.cpp

@@ -102,14 +102,15 @@ NS_INTERFACE_TABLE_TAIL_INHERITING(nsGenericHTMLFormElementWithState)
 // nsIDOMHTMLTextAreaElement
 
 nsresult
-HTMLTextAreaElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
+HTMLTextAreaElement::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                           bool aPreallocateChildren) const
 {
   *aResult = nullptr;
   already_AddRefed<mozilla::dom::NodeInfo> ni =
     RefPtr<mozilla::dom::NodeInfo>(aNodeInfo).forget();
   RefPtr<HTMLTextAreaElement> it = new HTMLTextAreaElement(ni);
 
-  nsresult rv = const_cast<HTMLTextAreaElement*>(this)->CopyInnerTo(it);
+  nsresult rv = const_cast<HTMLTextAreaElement*>(this)->CopyInnerTo(it, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   if (mValueChanged) {
@@ -1120,9 +1121,10 @@ HTMLTextAreaElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
   }
 
 nsresult
-HTMLTextAreaElement::CopyInnerTo(Element* aDest)
+HTMLTextAreaElement::CopyInnerTo(Element* aDest, bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLFormElementWithState::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLFormElementWithState::CopyInnerTo(aDest,
+                                                               aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   if (aDest->OwnerDoc()->IsStaticDocument()) {

dom/html/HTMLTextAreaElement.h

@@ -145,9 +145,10 @@ public:
   virtual void DoneAddingChildren(bool aHaveNotified) override;
   virtual bool IsDoneAddingChildren() override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
-  nsresult CopyInnerTo(Element* aDest);
+  nsresult CopyInnerTo(Element* aDest, bool aPreallocateChildren);
 
   /**
    * Called when an attribute is about to be changed

dom/html/HTMLTimeElement.h

@@ -32,7 +32,8 @@ public:
     SetHTMLAttr(nsGkAtoms::datetime, aDateTime, aError);
   }
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual JSObject* WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;

dom/html/HTMLTitleElement.h

@@ -38,7 +38,8 @@ public:
   NS_DECL_NSIMUTATIONOBSERVER_CONTENTINSERTED
   NS_DECL_NSIMUTATIONOBSERVER_CONTENTREMOVED
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual nsresult BindToTree(nsIDocument *aDocument, nsIContent *aParent,
                               nsIContent *aBindingParent,

dom/html/HTMLTrackElement.h

@@ -90,7 +90,8 @@ public:
 
   TextTrack* GetTrack();
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                         bool aPreallocateChildren) const override;
 
   // Override ParseAttribute() to convert kind strings to enum values.
   virtual bool ParseAttribute(int32_t aNamespaceID,

dom/html/HTMLUnknownElement.h

@@ -31,7 +31,8 @@ public:
     }
   }
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
 protected:
   virtual ~HTMLUnknownElement() {}

dom/html/HTMLVideoElement.h

@@ -41,7 +41,8 @@ public:
 
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
 
-  virtual nsresult Clone(NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // Set size with the current video frame's height and width.
   // If there is no video frame, returns NS_ERROR_FAILURE.

dom/html/nsGenericHTMLElement.cpp

@@ -175,9 +175,14 @@ NS_INTERFACE_MAP_BEGIN(nsGenericHTMLElement)
 NS_INTERFACE_MAP_END_INHERITING(nsGenericHTMLElementBase)
 
 nsresult
-nsGenericHTMLElement::CopyInnerTo(Element* aDst)
+nsGenericHTMLElement::CopyInnerTo(Element* aDst, bool aPreallocateChildren)
 {
   nsresult rv;
+
+  rv = static_cast<nsGenericHTMLElement*>(aDst)->mAttrsAndChildren.
+       EnsureCapacityToClone(mAttrsAndChildren, aPreallocateChildren);
+  NS_ENSURE_SUCCESS(rv, rv);
+
   int32_t i, count = GetAttrCount();
   for (i = 0; i < count; ++i) {
     const nsAttrName *name = mAttrsAndChildren.AttrNameAt(i);

dom/html/nsGenericHTMLElement.h

@@ -68,7 +68,7 @@ public:
   NS_IMPL_FROMCONTENT(nsGenericHTMLElement, kNameSpaceID_XHTML)
 
   // From Element
-  nsresult CopyInnerTo(mozilla::dom::Element* aDest);
+  nsresult CopyInnerTo(mozilla::dom::Element* aDest, bool aPreallocateChildren);
 
   void GetTitle(mozilla::dom::DOMString& aTitle)
   {

dom/html/nsGenericHTMLFrameElement.cpp

@@ -433,9 +433,10 @@ nsGenericHTMLFrameElement::DestroyContent()
 }
 
 nsresult
-nsGenericHTMLFrameElement::CopyInnerTo(Element* aDest)
+nsGenericHTMLFrameElement::CopyInnerTo(Element* aDest,
+                                       bool aPreallocateChildren)
 {
-  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
+  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest, aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   nsIDocument* doc = aDest->OwnerDoc();

dom/html/nsGenericHTMLFrameElement.h

@@ -68,7 +68,7 @@ public:
                                 bool aNotify) override;
   virtual void DestroyContent() override;
 
-  nsresult CopyInnerTo(mozilla::dom::Element* aDest);
+  nsresult CopyInnerTo(mozilla::dom::Element* aDest, bool aPreallocateChildren);
 
   virtual int32_t TabIndexDefault() override;
 

dom/html/nsHTMLDocument.cpp

@@ -3654,13 +3654,14 @@ nsHTMLDocument::QueryCommandValue(const nsAString& commandID,
 }
 
 nsresult
-nsHTMLDocument::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const
+nsHTMLDocument::Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                      bool aPreallocateChildren) const
 {
   NS_ASSERTION(aNodeInfo->NodeInfoManager() == mNodeInfoManager,
                "Can't import this document into another document!");
 
   RefPtr<nsHTMLDocument> clone = new nsHTMLDocument();
-  nsresult rv = CloneDocHelper(clone.get());
+  nsresult rv = CloneDocHelper(clone.get(), aPreallocateChildren);
   NS_ENSURE_SUCCESS(rv, rv);
 
   // State from nsHTMLDocument

dom/html/nsHTMLDocument.h

@@ -148,7 +148,8 @@ public:
 
   virtual nsresult SetEditingState(EditingState aState) override;
 
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   virtual void RemovedFromDocShell() override;
 

dom/mathml/nsMathMLElement.h

@@ -78,7 +78,8 @@ public:
                      mozilla::EventChainPreVisitor& aVisitor) override;
   virtual nsresult PostHandleEvent(
                      mozilla::EventChainPostVisitor& aVisitor) override;
-  nsresult Clone(mozilla::dom::NodeInfo*, nsINode**) const override;
+  nsresult Clone(mozilla::dom::NodeInfo* aNodeInfo, nsINode** aResult,
+                 bool aPreallocateChildren) const override;
   virtual mozilla::EventStates IntrinsicState() const override;
   virtual bool IsNodeOfType(uint32_t aFlags) const override;
 

dom/svg/SVGAElement.h

@@ -41,7 +41,8 @@ public:
                      EventChainPreVisitor& aVisitor) override;
   virtual nsresult PostHandleEvent(
                      EventChainPostVisitor& aVisitor) override;
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // nsIContent
   virtual nsresult BindToTree(nsIDocument *aDocument, nsIContent *aParent,

dom/svg/SVGAnimateElement.h

@@ -31,7 +31,8 @@ protected:
 
 public:
   // nsIDOMNode
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
+  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult,
+                         bool aPreallocateChildren) const override;
 
   // SVGAnimationElement
   virtual nsSMILAnimationFunction& AnimationFunction() override;