cc: nine patch: add occlusion support

cc/layers/nine_patch_layer.h

Index: cc/layers/nine_patch_layer.h
diff --git a/cc/layers/nine_patch_layer.h b/cc/layers/nine_patch_layer.h
index 1c2d7259e3e5b33e0f1cac97d13bc1839723b47e..accdc70437b005b3936a9c87b6bed370da782282 100644
--- a/cc/layers/nine_patch_layer.h
+++ b/cc/layers/nine_patch_layer.h
@@ -42,6 +42,11 @@ class CC_EXPORT NinePatchLayer : public UIResourceLayer {
   void SetFillCenter(bool fill_center);
   void SetNearestNeighbor(bool nearest_neighbor);
 
+  // |rect| is the space completely occluded by another layer in layer
+  // space. This can be used for example to occlude the entire window's
+  // content when drawing the shadow with a 9 patches layer.
+  void SetLayerOcclusion(const gfx::Rect& occlusion);
+
  private:
   NinePatchLayer();
   ~NinePatchLayer() override;
@@ -55,6 +60,10 @@ class CC_EXPORT NinePatchLayer : public UIResourceLayer {
   // image space.
   gfx::Rect image_aperture_;
 
+  // The occluded region in layer space set by SetLayerOcclusion. It is
+  // usually larger than |image_aperture_|.
+  gfx::Rect layer_occlusion_;
+
   DISALLOW_COPY_AND_ASSIGN(NinePatchLayer);
 };