Retain tray bubble's rounded corners when the bubble animates out

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index d308f607716629d1d0c2ea0cb6f74b39652bc062..975cb718fbab421b1afc182bb779878eaaf6bd08 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -196,13 +196,12 @@ class COMPOSITOR_EXPORT Layer
   // otherwise.
   float GetTargetOpacity() const;
 
-  // Set a layer mask for a layer.
+  // Set a layer mask for a layer. This transfers the ownership of |layer_mask|;
+  // a mask layer can only be transferred to one layer.
   // Note the provided layer mask can neither have a layer mask itself nor can
-  // it have any children. The ownership of |layer_mask| will not be
-  // transferred with this call.
-  // Furthermore: A mask layer can only be set to one layer.
-  void SetMaskLayer(Layer* layer_mask);
-  Layer* layer_mask_layer() { return layer_mask_; }
+  // it have any children.
+  void SetMaskLayer(scoped_ptr<Layer> layer_mask);
+  Layer* layer_mask_layer() { return layer_mask_.get(); }
 
   // Sets the visibility of the Layer. A Layer may be visible but not
   // drawn. This happens if any ancestor of a Layer is not visible.
@@ -449,12 +448,8 @@ class COMPOSITOR_EXPORT Layer
   float layer_grayscale_;
   bool layer_inverted_;
 
-  // The associated mask layer with this layer.
-  Layer* layer_mask_;
-  // The back link from the mask layer to it's associated masked layer.
-  // We keep this reference for the case that if the mask layer gets deleted
-  // while attached to the main layer before the main layer is deleted.
-  Layer* layer_mask_back_link_;
+  // The mask layer associated with this layer.
+  scoped_ptr<Layer> layer_mask_;
 
   // The zoom factor to scale the layer by.  Zooming is disabled when this is
   // set to 1.