Set up clip and scroll parents on the blink side.

Source/core/rendering/RenderLayerBacking.h

Index: Source/core/rendering/RenderLayerBacking.h
diff --git a/Source/core/rendering/RenderLayerBacking.h b/Source/core/rendering/RenderLayerBacking.h
index 5a18edd82084680b941763762d4d73e2e159268c..05fe25c81070892637ada7ed45969025a7fccadc 100644
--- a/Source/core/rendering/RenderLayerBacking.h
+++ b/Source/core/rendering/RenderLayerBacking.h
@@ -94,9 +94,12 @@ public:
     GraphicsLayer* clippingLayer() const { return m_childContainmentLayer.get(); }
 
     // Layer to get clipped by ancestor
-    bool hasAncestorClippingLayer() const { return m_ancestorClippingLayer != 0; }
+    bool hasAncestorClippingLayer() const { return m_ancestorClippingLayer; }
     GraphicsLayer* ancestorClippingLayer() const { return m_ancestorClippingLayer.get(); }
 
+    bool hasAncestorScrollClippingLayer() const { return m_ancestorScrollClippingLayer; }
+    GraphicsLayer* ancestorScrollClippingLayer() const { return m_ancestorScrollClippingLayer.get(); }
+
     bool hasContentsLayer() const { return m_foregroundLayer != 0; }
     GraphicsLayer* foregroundLayer() const { return m_foregroundLayer.get(); }
 
@@ -189,7 +192,7 @@ private:
     RenderLayerCompositor* compositor() const { return m_owningLayer->compositor(); }
 
     void updateInternalHierarchy();
-    bool updateClippingLayers(bool needsAncestorClip, bool needsDescendantClip);
+    bool updateClippingLayers(bool needsAncestorClip, bool needsDescendantClip, bool needsScrollClip);
     bool updateOverflowControlsLayers(bool needsHorizontalScrollbarLayer, bool needsVerticalScrollbarLayer, bool needsScrollCornerLayer);
     bool updateForegroundLayer(bool needsForegroundLayer);
     bool updateBackgroundLayer(bool needsBackgroundLayer);
@@ -198,6 +201,8 @@ private:
     bool requiresVerticalScrollbarLayer() const { return m_owningLayer->verticalScrollbar(); }
     bool requiresScrollCornerLayer() const { return !m_owningLayer->scrollCornerAndResizerRect().isEmpty(); }
     bool updateScrollingLayers(bool scrollingLayers);
+    void updateScrollParent(bool needsScrollParent);
+    void updateClipParent(bool needsAncestorClip);
     void updateDrawsContent(bool isSimpleContainer);
     void registerScrollingLayers();
 
@@ -247,6 +252,7 @@ private:
 
     RenderLayer* m_owningLayer;
 
+    OwnPtr<GraphicsLayer> m_ancestorScrollClippingLayer; // Only used if we have a scroll parent, and our clipping ancestor is not our scroll parent.
     OwnPtr<GraphicsLayer> m_ancestorClippingLayer; // Only used if we are clipped by an ancestor which is not a stacking context.
     OwnPtr<GraphicsLayer> m_graphicsLayer;
     OwnPtr<GraphicsLayer> m_foregroundLayer; // Only used in cases where we need to draw the foreground separately.
@@ -261,8 +267,6 @@ private:
     OwnPtr<GraphicsLayer> m_scrollingLayer; // Only used if the layer is using composited scrolling.
     OwnPtr<GraphicsLayer> m_scrollingContentsLayer; // Only used if the layer is using composited scrolling.
 
-    uint64_t m_scrollLayerID;
-
     IntRect m_compositedBounds;
 
     bool m_artificiallyInflatedBounds; // bounds had to be made non-zero to make transform-origin work