Land layer squashing behind a flag

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 10664284379c1adaebc8403faa2cab8240f69c02..6766c62e5cd95aa60f7d949b43809da630cc6cd3 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -354,6 +354,9 @@ public:
     bool hasCompositedLayerMapping() const { return m_compositedLayerMapping.get(); }
     void clearCompositedLayerMapping(bool layerBeingDestroyed = false);
 
+    CompositedLayerMapping* groupedMapping() const { return m_groupedMapping; }
+    void setGroupedMapping(CompositedLayerMapping* groupedMapping) { m_groupedMapping = groupedMapping; }
+
     bool hasCompositedMask() const;
     bool hasCompositedClippingMask() const;
     bool needsCompositedScrolling() const { return m_scrollableArea && m_scrollableArea->needsCompositedScrolling(); }
@@ -444,6 +447,9 @@ public:
 
     PassOwnPtr<Vector<FloatRect> > collectTrackedRepaintRects() const;
 
+    void setOffsetFromSquashingLayerOrigin(IntSize offset) { m_compositingProperties.offsetFromSquashingLayerOrigin = offset; }
+    IntSize offsetFromSquashingLayerOrigin() const { return m_compositingProperties.offsetFromSquashingLayerOrigin; }
+
 private:
     bool hasOverflowControls() const;
 
@@ -717,6 +723,9 @@ protected:
 
         // Once computed, indicates all that a layer needs to become composited using the CompositingReasons enum bitfield.
         CompositingReasons compositingReasons;
+
+        // Used for invalidating this layer's contents on the squashing GraphicsLayer.
+        IntSize offsetFromSquashingLayerOrigin;
     };
 
     CompositingProperties m_compositingProperties;
@@ -734,6 +743,8 @@ private:
     OwnPtr<CompositedLayerMapping> m_compositedLayerMapping;
     OwnPtr<RenderLayerScrollableArea> m_scrollableArea;
 
+    CompositedLayerMapping* m_groupedMapping;
+
     RenderLayerRepainter m_repainter;
     RenderLayerClipper m_clipper; // FIXME: Lazily allocate?
     OwnPtr<RenderLayerStackingNode> m_stackingNode;