Large canvas does not honor containing div's border radius

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 ffb48b44bf5f0e01c17096446b53e45d314d0045..e43acda963a9762eef3336dad75a5847793ec559 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -607,6 +607,7 @@ public:
         PaintLayerPaintingOverflowContents = 1 << 9,
         PaintLayerPaintingRootBackgroundOnly = 1 << 10,
         PaintLayerPaintingSkipRootBackground = 1 << 11,
+        PaintLayerPaintingCompositingBorderRadiusMaskPhase = 1 << 12,
         PaintLayerPaintingCompositingAllPhases = (PaintLayerPaintingCompositingBackgroundPhase | PaintLayerPaintingCompositingForegroundPhase | PaintLayerPaintingCompositingMaskPhase)
     };
     
@@ -738,6 +739,7 @@ public:
 
     bool isComposited() const { return m_backing != 0; }
     bool hasCompositedMask() const;
+    bool hasCompositedBorderRadiusMask() const;
     RenderLayerBacking* backing() const { return m_backing.get(); }
     RenderLayerBacking* ensureBacking();
     void clearBacking(bool layerBeingDestroyed = false);
@@ -963,7 +965,7 @@ private:
     void paintForegroundForFragmentsWithPhase(PaintPhase, const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer);
     void paintOutlineForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer);
     void paintOverflowControlsForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&);
-    void paintMaskForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, RenderObject* paintingRootForRenderer);
+    void paintMaskForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, RenderObject* paintingRootForRenderer, PaintPhase = PaintPhaseMask);
     void paintTransformedLayerIntoFragments(GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
 
     RenderLayer* hitTestLayer(RenderLayer* rootLayer, RenderLayer* containerLayer, const HitTestRequest& request, HitTestResult& result,