Replace the current contiguity check for composited scrolling

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index 2d25f1259d03b137778671299c047576fa4d3abc..5a3f5747b3eb2fa93d85a87dbb152c703f53d547 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -843,8 +843,7 @@ private:
     void dirtyAncestorChainHasOutOfFlowPositionedDescendantStatus();
 
     bool acceleratedCompositingForOverflowScrollEnabled() const;
-    void updateDescendantsAreContiguousInStackingOrder();
-    void updateDescendantsAreContiguousInStackingOrderRecursive(const HashMap<const RenderLayer*, int>&, int& minIndex, int& maxIndex, int& count, bool firstIteration);
+    void updateCanBeStackingContainer();
     void collectBeforePromotionZOrderList(RenderLayer* ancestorStackingContext, OwnPtr<Vector<RenderLayer*> >& posZOrderListBeforePromote, OwnPtr<Vector<RenderLayer*> >& negZOrderListBeforePromote);
     void collectAfterPromotionZOrderList(RenderLayer* ancestorStackingContext, OwnPtr<Vector<RenderLayer*> >& posZOrderListAfterPromote, OwnPtr<Vector<RenderLayer*> >& negZOrderListAfterPromote);
 
@@ -1149,8 +1148,8 @@ 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_descendantsAreContiguousInStackingOrderDirty : 1;
+    bool m_canBePromotedToStackingContainer : 1;
+    bool m_canBePromotedToStackingContainerDirty : 1;
 
     const bool m_isRootLayer : 1;