mus drag and drop: return the completed effect to the caller.

services/ui/public/cpp/window_tree_client.h

Index: services/ui/public/cpp/window_tree_client.h
diff --git a/services/ui/public/cpp/window_tree_client.h b/services/ui/public/cpp/window_tree_client.h
index 93d3e5303366ee8f8388a06737e53886f138af58..d6c9fbf2d3a9a9c353cdb58d60dd69a7f729a51c 100644
--- a/services/ui/public/cpp/window_tree_client.h
+++ b/services/ui/public/cpp/window_tree_client.h
@@ -183,7 +183,7 @@ class WindowTreeClient : public mojom::WindowTreeClient,
       int drag_operation,
       const gfx::Point& cursor_location,
       const SkBitmap& bitmap,
-      const base::Callback<void(bool)>& callback);
+      const base::Callback<void(bool, uint32_t)>& callback);
 
   // Performs a window move. |callback| will be asynchronously called with the
   // whether the move loop completed successfully.
@@ -338,6 +338,9 @@ class WindowTreeClient : public mojom::WindowTreeClient,
                       const gfx::Point& position,
                       uint32_t effect_bitmask,
                       const OnCompleteDropCallback& callback) override;
+  void OnPerformDragDropCompleted(uint32_t window,
+                                  bool success,
+                                  uint32_t action_taken) override;
   void OnDragDropDone() override;
   void OnChangeCompleted(uint32_t change_id, bool success) override;
   void RequestClose(uint32_t window_id) override;