Bug 1596199 - Devirtualize GetBindingParent. r=bzbarsky

The amount of XUL elements with non-null binding-parent pointer should be
equivalent to HTML now that XBL is gone.

Shadow DOM already has the extended slots for both the binding parent and
containing shadow root.

Differential Revision: https://phabricator.services.mozilla.com/D52901

--HG--
extra : moz-landing-system : lando

dom/base/Element.cpp

@@ -1477,16 +1477,9 @@ nsresult Element::BindToTree(BindContext& aContext, nsINode& aParent) {
                      aParent.AsContent()->GetBindingParent(),
              "We should be passed the right binding parent");
 
-#ifdef MOZ_XUL
   // First set the binding parent
-  if (nsXULElement* xulElem = nsXULElement::FromNode(this)) {
-    xulElem->SetXULBindingParent(aContext.GetBindingParent());
-  } else
-#endif
-  {
-    if (Element* bindingParent = aContext.GetBindingParent()) {
-      ExtendedDOMSlots()->mBindingParent = bindingParent;
-    }
+  if (Element* bindingParent = aContext.GetBindingParent()) {
+    ExtendedDOMSlots()->mBindingParent = bindingParent;
   }
 
   const bool hadParent = !!GetParentNode();
@@ -1771,19 +1764,8 @@ void Element::UnbindFromTree(bool aNullParent) {
     SetSubtreeRootPointer(aNullParent ? this : mParent->SubtreeRoot());
   }
 
-  bool clearBindingParent = true;
-
-#ifdef MOZ_XUL
-  if (nsXULElement* xulElem = nsXULElement::FromNode(this)) {
-    xulElem->SetXULBindingParent(nullptr);
-    clearBindingParent = false;
-  }
-#endif
-
   if (nsExtendedDOMSlots* slots = GetExistingExtendedDOMSlots()) {
-    if (clearBindingParent) {
-      slots->mBindingParent = nullptr;
-    }
+    slots->mBindingParent = nullptr;
     if (aNullParent || !mParent->IsInShadowTree()) {
       slots->mContainingShadow = nullptr;
     }

dom/base/nsIContent.h

@@ -382,14 +382,14 @@ class nsIContent : public nsINode {
   /**
    * Gets content node with the binding (or native code, possibly on the
    * frame) responsible for our construction (and existence).  Used by
-   * anonymous content (both XBL-generated and native-anonymous).
+   * native-anonymous content and shadow DOM.
    *
    * null for all explicit content (i.e., content reachable from the top
    * of its GetParent() chain via child lists).
    *
    * @return the binding parent
    */
-  virtual mozilla::dom::Element* GetBindingParent() const {
+  mozilla::dom::Element* GetBindingParent() const {
     const nsExtendedContentSlots* slots = GetExistingExtendedContentSlots();
     return slots ? slots->mBindingParent.get() : nullptr;
   }

dom/xul/nsXULElement.cpp

@@ -103,7 +103,7 @@ uint32_t nsXULPrototypeAttribute::gNumCacheFills;
 //
 
 nsXULElement::nsXULElement(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
-    : nsStyledElement(std::move(aNodeInfo)), mBindingParent(nullptr) {
+    : nsStyledElement(std::move(aNodeInfo)) {
   XUL_PROTOTYPE_ATTRIBUTE_METER(gNumElements);
 }
 
@@ -271,17 +271,7 @@ void NS_TrustedNewXULElement(
 //----------------------------------------------------------------------
 // nsISupports interface
 
-NS_IMPL_CYCLE_COLLECTION_CLASS(nsXULElement)
-
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsXULElement, nsStyledElement)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mBindingParent);
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
-
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsXULElement, nsStyledElement)
-  // Why aren't we unlinking the prototype?
-  tmp->ClearHasID();
-  NS_IMPL_CYCLE_COLLECTION_UNLINK(mBindingParent);
-NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_INHERITED(nsXULElement, nsStyledElement)
 
 NS_IMPL_ADDREF_INHERITED(nsXULElement, nsStyledElement)
 NS_IMPL_RELEASE_INHERITED(nsXULElement, nsStyledElement)

dom/xul/nsXULElement.h

@@ -349,8 +349,6 @@ class nsXULElement : public nsStyledElement {
                                 bool aIsTrustedEvent) override;
   void ClickWithInputSource(uint16_t aInputSource, bool aIsTrustedEvent);
 
-  Element* GetBindingParent() const final { return mBindingParent; }
-
   virtual bool IsNodeOfType(uint32_t aFlags) const override;
   virtual bool IsFocusableInternal(int32_t* aTabIndex,
                                    bool aWithMouse) override;
@@ -364,13 +362,6 @@ class nsXULElement : public nsStyledElement {
 
   virtual void RecompileScriptEventListeners() override;
 
-  // This function should ONLY be used by BindToTree implementations.
-  // The function exists solely because XUL elements store the binding
-  // parent as a member instead of in the slots, as Element does.
-  void SetXULBindingParent(Element* aBindingParent) {
-    mBindingParent = aBindingParent;
-  }
-
   virtual bool IsEventAttributeNameInternal(nsAtom* aName) override;
 
   typedef mozilla::dom::DOMString DOMString;
@@ -532,12 +523,6 @@ class nsXULElement : public nsStyledElement {
 
   nsresult AddPopupListener(nsAtom* aName);
 
-  /**
-   * The nearest enclosing content node with a binding
-   * that created us.
-   */
-  RefPtr<Element> mBindingParent;
-
   /**
    * Abandon our prototype linkage, and copy all attributes locally
    */