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 a9acf7a00141d94de60c75178c0b734ec26c9a48..b64c895b671e9634d66bf2e0d951bc241e8cca2a 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -839,8 +839,8 @@ private:
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
     bool acceleratedCompositingForOverflowScrollEnabled() const;
-    void updateDescendantsAreContiguousInStackingOrder();
-    void updateDescendantsAreContiguousInStackingOrderRecursive(const HashMap<const RenderLayer*, int>&, int& minIndex, int& maxIndex, int& count, bool firstIteration);
+    void updateCanBeStackingContainer(RenderLayer*);
+    void updateCanBeStackingContainerRecursively(RenderLayer*);
     void collectBeforePromotionZOrderList(RenderLayer* ancestorStackingContext, OwnPtr<Vector<RenderLayer*> >& posZOrderListBeforePromote, OwnPtr<Vector<RenderLayer*> >& negZOrderListBeforePromote, size_t& posZOrderListSizeBeforePromote, size_t& negZOrderListSizeBeforePromote);
     void collectAfterPromotionZOrderList(RenderLayer* ancestorStackingContext, OwnPtr<Vector<RenderLayer*> >& posZOrderListAfterPromote, OwnPtr<Vector<RenderLayer*> >& negZOrderListAfterPromote, size_t& posZOrderListSizeAfterPromote, size_t& negZOrderListSizeAfterPromote);
 
@@ -1141,8 +1141,8 @@ 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;