Bug 496823. Blocks can implement GetLastChild() much faster than by just getting first child and iterating its siblings. r=roc

layout/base/nsCSSFrameConstructor.cpp

@@ -5725,13 +5725,13 @@ AdjustAppendParentForAfterContent(nsPresContext* aPresContext,
 static nsIFrame*
 FindAppendPrevSibling(nsIFrame* aParentFrame, nsIFrame* aAfterFrame)
 {
-  nsFrameList childList(aParentFrame->GetFirstChild(nsnull));
   if (aAfterFrame) {
+    nsFrameList childList(aParentFrame->GetFirstChild(nsnull));
     NS_ASSERTION(aAfterFrame->GetParent() == aParentFrame, "Wrong parent");
     return childList.GetPrevSiblingFor(aAfterFrame);
   }
 
-  return childList.LastChild();
+  return aParentFrame->GetLastChild(nsnull);
 }
 
 /**

layout/generic/nsBlockFrame.cpp

@@ -538,6 +538,20 @@ nsBlockFrame::GetFirstChild(nsIAtom* aListName) const
   return nsContainerFrame::GetFirstChild(aListName);;
 }
 
+nsIFrame*
+nsBlockFrame::GetLastChild(nsIAtom* aListName) const
+{
+  if (aListName) {
+    return nsBlockFrameSuper::GetLastChild(aListName);
+  }
+
+  if (mLines.empty()) {
+    return nsnull;
+  }
+
+  return mLines.back()->LastChild();
+}
+
 #define NS_BLOCK_FRAME_OVERFLOW_OOF_LIST_INDEX  (NS_CONTAINER_LIST_COUNT_INCL_OC + 0)
 #define NS_BLOCK_FRAME_FLOAT_LIST_INDEX         (NS_CONTAINER_LIST_COUNT_INCL_OC + 1)
 #define NS_BLOCK_FRAME_BULLET_LIST_INDEX        (NS_CONTAINER_LIST_COUNT_INCL_OC + 2)

layout/generic/nsBlockFrame.h

@@ -177,6 +177,7 @@ public:
   NS_IMETHOD  RemoveFrame(nsIAtom*        aListName,
                           nsIFrame*       aOldFrame);
   virtual nsIFrame* GetFirstChild(nsIAtom* aListName) const;
+  virtual nsIFrame* GetLastChild(nsIAtom* aListName) const;
   virtual nscoord GetBaseline() const;
   virtual nsIAtom* GetAdditionalChildListName(PRInt32 aIndex) const;
   virtual void Destroy();

layout/generic/nsFrame.cpp

@@ -1667,6 +1667,12 @@ nsIFrame::CreateWidgetForView(nsIView* aView)
   return aView->CreateWidget(kWidgetCID);
 }
 
+nsIFrame*
+nsIFrame::GetLastChild(nsIAtom* aListName) const
+{
+  return nsLayoutUtils::GetLastSibling(GetFirstChild(aListName));
+}
+
 /**
   *
  */

layout/generic/nsIFrame.h

@@ -856,6 +856,16 @@ public:
    */
   virtual nsIFrame* GetFirstChild(nsIAtom* aListName) const = 0;
 
+  /**
+   * Get the last child frame from the specified child list.
+   *
+   * @param   aListName the name of the child list. A NULL pointer for the atom
+   *            name means the unnamed principal child list
+   * @return  the child frame, or NULL if there is no such child
+   * @see     #GetAdditionalListName()
+   */
+  virtual nsIFrame* GetLastChild(nsIAtom* aListName) const;
+
   /**
    * Child frames are linked together in a singly-linked list
    */