cc: Support mask layers in impl-side painting

cc/picture_layer.h

Index: cc/picture_layer.h
diff --git a/cc/picture_layer.h b/cc/picture_layer.h
index fd330fba34e621f26f4300c4d9dece93f22fea78..2ff522f40bc28dcb6f258d6cc24e6ab27bebe986 100644
--- a/cc/picture_layer.h
+++ b/cc/picture_layer.h
@@ -30,6 +30,7 @@ public:
   virtual void setNeedsDisplayRect(const gfx::RectF& layerRect) OVERRIDE;
   virtual void update(ResourceUpdateQueue&, const OcclusionTracker*,
                       RenderingStats&) OVERRIDE;
+  virtual void setIsMask(bool is_mask) OVERRIDE;
 
 protected:
   explicit PictureLayer(ContentLayerClient*);
@@ -42,6 +43,7 @@ private:
   Region pending_invalidation_;
   // Invalidation from the last time update was called.
   Region pile_invalidation_;
+  bool is_mask_;
 };
 
 }  // namespace cc