Get rid of one-off code in ScrollingCoordinator to handle graphics layer offsets.

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 c3635f19261d259341f4a4806dc4b33e3c30195e..c7a3efdb424a2ce8923ab4abfa559cb1971370a6 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -341,6 +341,8 @@ public:
     // This will allow us to clean up this static method messiness.
     static LayoutPoint positionFromPaintInvalidationContainer(const RenderObject*, const RenderLayerModelObject* paintInvalidationContainer);
 
+    static void mapRectToPaintBackingCoordinates(const RenderLayerModelObject* paintInvalidationContainer, LayoutRect&);
+
     // Adjusts the given rect (in the coordinate space of the RenderObject) to the coordinate space of |paintInvalidationContainer|'s GraphicsLayer backing.
     static void mapRectToPaintInvalidationBacking(const RenderObject*, const RenderLayerModelObject* paintInvalidationContainer, LayoutRect&);
 
@@ -432,9 +434,6 @@ public:
 
     RenderLayerBlendInfo& blendInfo() { return m_blendInfo; }
 
-    void setOffsetFromSquashingLayerOrigin(IntSize offset) { m_offsetFromSquashingLayerOrigin = offset; }
-    IntSize offsetFromSquashingLayerOrigin() const { ASSERT(isAllowedToQueryCompositingState()); return m_offsetFromSquashingLayerOrigin; }
-
     bool scrollsOverflow() const;
 
     CompositingReasons potentialCompositingReasonsFromStyle() const { return m_potentialCompositingReasonsFromStyle; }
@@ -708,9 +707,6 @@ private:
     // Once computed, indicates all that a layer needs to become composited using the CompositingReasons enum bitfield.
     CompositingReasons m_compositingReasons;
 
-    // Used for invalidating this layer's contents on the squashing GraphicsLayer.
-    IntSize m_offsetFromSquashingLayerOrigin;
-
     CompositingInputs m_compositingInputs;
 
     IntRect m_blockSelectionGapsBounds;