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 c0eac436e6609ef004ac28679b631e57d3d3f0f7..8ca5d91ab9c8e0656a00a54e3ac7410a34130fae 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -436,7 +436,7 @@ public:
     virtual void detach(const AttachContext& = AttachContext()) OVERRIDE;
     virtual RenderObject* createRenderer(RenderStyle*);
     virtual bool rendererIsNeeded(const NodeRenderingContext&);
-    bool recalcStyle(StyleChange = NoChange);
+    bool recalcStyle(StyleChange = NoChange, int childIndex = 0);
     void didAffectSelector(AffectedSelectorMask);
 
     ElementShadow* shadow() const;
@@ -608,8 +608,8 @@ 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;
     virtual bool shouldMoveToFlowThread(RenderStyle*) const;