Make squashing work with subpixel layout

Source/core/rendering/CompositedLayerMapping.h

Index: Source/core/rendering/CompositedLayerMapping.h
diff --git a/Source/core/rendering/CompositedLayerMapping.h b/Source/core/rendering/CompositedLayerMapping.h
index 2b6855091a1c3c5989d4a1dfad6267d13415c2d2..50d2e229f202d7569f2c3ebf1d04ca9094e32165 100644
--- a/Source/core/rendering/CompositedLayerMapping.h
+++ b/Source/core/rendering/CompositedLayerMapping.h
@@ -56,7 +56,7 @@ struct GraphicsLayerPaintInfo {
     // an intermediate offset for a squashed RenderLayer, described with respect to the CompositedLayerMapping's
     // owning layer that would eventually have the m_squashingLayer. Once the shared GraphicsLayer's bounds are
     // known, then we can trivially convert this offset to m_squashingLayer's space.
-    IntSize offsetFromSquashingCLM;
+    LayoutSize offsetFromSquashingCLM;
 
     // Offset describing where this squashed RenderLayer paints into the shared GraphicsLayer backing.
     IntSize offsetFromRenderer;
@@ -154,7 +154,7 @@ public:
     void positionOverflowControlsLayers(const IntSize& offsetFromRoot);
     bool hasUnpositionedOverflowControlsLayers() const;
 
-    void addRenderLayerToSquashingGraphicsLayer(RenderLayer*, IntSize offsetFromSquashingCLM, size_t nextSquashedLayerIndex);
+    void addRenderLayerToSquashingGraphicsLayer(RenderLayer*, LayoutSize offsetFromSquashingCLM, size_t nextSquashedLayerIndex);
     void finishAccumulatingSquashingLayers(size_t nextSquashedLayerIndex);
 
     // GraphicsLayerClient interface