cc: nine patch: add occlusion support

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index 95c72a06dd0261365d4e5cac9aea96ad3fdaef4d..c19e8eab056130dc0e79971abfe0e6b979465510 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -321,6 +321,9 @@ class COMPOSITOR_EXPORT Layer
   void UpdateNinePatchLayerImage(const gfx::ImageSkia& image);
   void UpdateNinePatchLayerAperture(const gfx::Rect& aperture_in_dip);
   void UpdateNinePatchLayerBorder(const gfx::Rect& border);
+  // Updates the area completely occluded by another layer, this can be an
+  // empty rectangle if nothing is occluded.
+  void UpdateNinePatchOcclusion(const gfx::Rect& occlusion);
 
   // Adds |invalid_rect| to the Layer's pending invalid rect and calls
   // ScheduleDraw(). Returns false if the paint request is ignored.