Revert 151996 "Avoid N^2 walk placing renderers when building th..."

Source/core/css/SelectorChecker.h

Index: Source/core/css/SelectorChecker.h
diff --git a/Source/core/css/SelectorChecker.h b/Source/core/css/SelectorChecker.h
index 30b7f9edc4fb10df2e63182f98341d36533e7ead..2b192e755d1478e5457e0a306bec3f0eb35af2c2 100644
--- a/Source/core/css/SelectorChecker.h
+++ b/Source/core/css/SelectorChecker.h
@@ -58,7 +58,7 @@ public:
 
     struct SelectorCheckingContext {
         // Initial selector constructor
-        SelectorCheckingContext(const CSSSelector* selector, Element* element, VisitedMatchType visitedMatchType, int childIndex = 0)
+        SelectorCheckingContext(const CSSSelector* selector, Element* element, VisitedMatchType visitedMatchType)
             : selector(selector)
             , element(element)
             , scope(0)
@@ -71,7 +71,6 @@ public:
             , hasScrollbarPseudo(false)
             , hasSelectionPseudo(false)
             , behaviorAtBoundary(DoesNotCrossBoundary)
-            , childIndex(childIndex)
         { }
 
         const CSSSelector* selector;
@@ -86,7 +85,6 @@ public:
         bool hasScrollbarPseudo;
         bool hasSelectionPseudo;
         BehaviorAtBoundary behaviorAtBoundary;
-        int childIndex;
     };
 
     template<typename SiblingTraversalStrategy>