Hides ink ripple when a button drag is started

ui/views/view.h

Index: ui/views/view.h
diff --git a/ui/views/view.h b/ui/views/view.h
index ec070e55cec57713cecd60cf20badc83654c4a3d..45231f53e7746db8148bd4e47a44347d7b4dce61 100644
--- a/ui/views/view.h
+++ b/ui/views/view.h
@@ -936,6 +936,10 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   // operation and the user release the mouse.
   virtual int OnPerformDrop(const ui::DropTargetEvent& event);
 
+  // Invoked from DoDrag when the drag starts. This implementation does
+  // nothing, and is intended for subclasses to do setup.
+  virtual void OnDragStarted(const ui::LocatedEvent& event);
+
   // Invoked from DoDrag after the drag completes. This implementation does
   // nothing, and is intended for subclasses to do cleanup.
   virtual void OnDragDone();