Add ink drop masking to TrayBackgroundView

ui/views/animation/ink_drop.h

Index: ui/views/animation/ink_drop.h
diff --git a/ui/views/animation/ink_drop.h b/ui/views/animation/ink_drop.h
index 1de593fef9213b4f5990ac8bf52dce177d620771..4e06c6923463ce7042e3af74695f260a9a7f20d7 100644
--- a/ui/views/animation/ink_drop.h
+++ b/ui/views/animation/ink_drop.h
@@ -24,6 +24,9 @@ class VIEWS_EXPORT InkDrop {
  public:
   virtual ~InkDrop() {}
 
+  // Used to update the layer size for the ink drop.
+  virtual void UpdateLayerSize(const gfx::Size& layer_size) = 0;

[bruthig, 2016/11/14 19:09:38]

I think this would be better named as "HostSizeChanged()".  Client's shouldn't
need to be aware about the underlying Layer or it's size. And the docs should
tell clients when it needs to be called.

[mohsen, 2016/11/14 20:19:39]

Sure. Done.

+
   // Gets the target state of the ink drop.
   virtual InkDropState GetTargetInkDropState() const = 0;