Fix pixel snapping issues when layers become composited

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 273fd3fe4245cbb49b4f77fd85c7e13cee65715b..7215cef58c661eae6c628131558cf49299e3d741 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -296,7 +296,7 @@ public:
     bool overlapBoundsIncludeChildren() const { return hasFilter() && renderer()->style()->filter().hasFilterThatMovesPixels(); }
 
     // Can pass offsetFromRoot if known.
-    IntRect calculateLayerBounds(const RenderLayer* ancestorLayer, const LayoutPoint* offsetFromRoot = 0, CalculateLayerBoundsFlags = DefaultCalculateLayerBoundsFlags) const;
+    LayoutRect calculateLayerBounds(const RenderLayer* ancestorLayer, const LayoutPoint* offsetFromRoot = 0, CalculateLayerBoundsFlags = DefaultCalculateLayerBoundsFlags) const;
 
     // WARNING: This method returns the offset for the parent as this is what updateLayerPositions expects.
     LayoutPoint computeOffsetFromRoot(bool& hasLayerOffset) const;
@@ -501,7 +501,8 @@ private:
 
     void collectFragments(LayerFragments&, const RenderLayer* rootLayer, RenderRegion*, const LayoutRect& dirtyRect,
         ClipRectsType, OverlayScrollbarSizeRelevancy inOverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize,
-        ShouldRespectOverflowClip = RespectOverflowClip, const LayoutPoint* offsetFromRoot = 0, const LayoutRect* layerBoundingBox = 0);
+        ShouldRespectOverflowClip = RespectOverflowClip, const LayoutPoint* offsetFromRoot = 0,
+        const LayoutSize& subPixelAccumulation = LayoutSize(), const LayoutRect* layerBoundingBox = 0);
     void updatePaintingInfoForFragments(LayerFragments&, const LayerPaintingInfo&, PaintLayerFlags, bool shouldPaintContent, const LayoutPoint* offsetFromRoot);
     void paintBackgroundForFragments(const LayerFragments&, GraphicsContext*, GraphicsContext* transparencyLayerContext,
         const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer);