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

Source/core/css/resolver/StyleResolverState.cpp

Index: Source/core/css/resolver/StyleResolverState.cpp
diff --git a/Source/core/css/resolver/StyleResolverState.cpp b/Source/core/css/resolver/StyleResolverState.cpp
index 61078a8cad13e79cff0ac412e8a4845acd3fe4f2..4ab3ab0c2b67a854062baf69927bf1e2cdc37a1d 100644
--- a/Source/core/css/resolver/StyleResolverState.cpp
+++ b/Source/core/css/resolver/StyleResolverState.cpp
@@ -44,6 +44,7 @@ void StyleResolverState::cacheBorderAndBackground()
 void StyleResolverState::clear()
 {
     m_element = 0;
+    m_childIndex = 0;
     m_styledElement = 0;
     m_parentStyle = 0;
     m_parentNode = 0;
@@ -53,9 +54,10 @@ void StyleResolverState::clear()
     m_pendingSVGDocuments.clear();
 }
 
-void StyleResolverState::initElement(Element* e)
+void StyleResolverState::initElement(Element* e, int childIndex)
 {
     m_element = e;
+    m_childIndex = childIndex;
     m_styledElement = e && e->isStyledElement() ? e : 0;
     m_elementLinkState = e ? e->document()->visitedLinkState()->determineLinkState(e) : NotInsideLink;
 }