Replace the current contiguity check for composited scrolling

Source/WebCore/rendering/RenderLayer.h

Index: Source/WebCore/rendering/RenderLayer.h
diff --git a/Source/WebCore/rendering/RenderLayer.h b/Source/WebCore/rendering/RenderLayer.h
index 5bb7fe34d15e20d896ec4d2def198cdcde31eda3..03403c5372112782ce89f8063d7377c5a986cb95 100644
--- a/Source/WebCore/rendering/RenderLayer.h
+++ b/Source/WebCore/rendering/RenderLayer.h
@@ -858,13 +858,13 @@ private:
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
     bool acceleratedCompositingForOverflowScrollEnabled() const;
-    void updateDescendantsAreContiguousInStackingOrder();
-    void updateDescendantsAreContiguousInStackingOrderRecursive(const HashMap<const RenderLayer*, int>&, int& minIndex, int& maxIndex, int& count, bool firstIteration);
     void collectBeforeAfterPromotionZOrderLists(RenderLayer* ancestorStackingContext,
         OwnPtr<Vector<RenderLayer*> >& posZOrderListBeforePromote,
         OwnPtr<Vector<RenderLayer*> >& negZOrderListBeforePromote,
         OwnPtr<Vector<RenderLayer*> >& posZOrderListAfterPromote,
         OwnPtr<Vector<RenderLayer*> >& negZOrderListAfterPromote);
+    void updateCanBeStackingContainer(RenderLayer*);
+    void updateCanBeStackingContainerRecursively(RenderLayer*);
     void getPaintOrderLists(RenderLayer* ancestorStackingContext,
         OwnPtr<Vector<RenderLayer*> >& posZOrderListBeforePromote,
         OwnPtr<Vector<RenderLayer*> >& negZOrderListBeforePromote,
@@ -1171,7 +1171,7 @@ protected:
     // If this is true, then no non-descendant appears between any of our
     // descendants in stacking order. This is one of the requirements of being
     // able to safely become a stacking context.
-    bool m_descendantsAreContiguousInStackingOrder : 1;
+    bool m_canBePromotedToStackingContainer : 1;
 
     const bool m_isRootLayer : 1;