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 28e5a7c4aaf02ee4f7a0178160728b566f267673..5176d288867d39c4e05b7423fbce398cd724ec58 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;
@@ -575,8 +575,8 @@ 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;