Avoid N^2 walk placing renderers when building the render tree

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index 8fafa3e4db1e5d59df792c4727ba9a53c2ae7911..669782c80666d1af6bab2611fa6110d12113782c 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -410,7 +410,7 @@ public:
     virtual void detach();
     virtual RenderObject* createRenderer(RenderArena*, RenderStyle*);
     virtual bool rendererIsNeeded(const NodeRenderingContext&);
-    void recalcStyle(StyleChange = NoChange);
+    void recalcStyle(StyleChange = NoChange, int childIndex = 0);
     void didAffectSelector(AffectedSelectorMask);
 
     ElementShadow* shadow() const;
@@ -576,8 +576,8 @@ public:
 
     bool isSpellCheckingEnabled() const;
 
-    PassRefPtr<RenderStyle> styleForRenderer();
-    PassRefPtr<RenderStyle> originalStyleForRenderer();
+    PassRefPtr<RenderStyle> styleForRenderer(int childIndex = 0);
+    PassRefPtr<RenderStyle> originalStyleForRenderer(int childIndex = 0);
 
     RenderRegion* renderRegion() const;
     const AtomicString& webkitRegionOverset() const;