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

services/ui/public/interfaces/window_tree.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module ui.mojom;
 
 import "cc/ipc/surface_id.mojom";
 import "services/ui/public/interfaces/cursor.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
 import "services/ui/public/interfaces/mus_constants.mojom";
@@ skipping 432 matching lines @@
 
   // Called when the pointer leaves a window or if the drop is
   // canceled.
   OnDragLeave(uint32 window);
 
   // Called when the drop occurs on a window. Returns the action
   // taken.
   OnCompleteDrop(uint32 window,
                  uint32 key_state,
                  gfx.mojom.Point position,
-                 uint32 effect_bitmask) => (uint32 effect_taken);
+                 uint32 effect_bitmask) => (uint32 action_taken);
 
-  // Called after OnDragDrop completes for every connection which received an
-  // OnDragDropStart() message. This signals that a client can forget the
+  // Called on the client that requested PerformDragDrop() to return which drag
+  // action was completed. This is called instead of OnChangeCompleted().
+  OnPerformDragDropCompleted(uint32 window, bool success, uint32 action_taken);
+
+  // Called after OnCompleteDrop completes for every connection which received
+  // an OnDragDropStart() message. This signals that a client can forget the
   // |drag_data| passed in via the first message.
   OnDragDropDone();
 
   // A change initiated from the client has completed. See description of
   // change ids for details.
   OnChangeCompleted(uint32 change_id, bool success);
 
   // The WindowManager is requesting the specified window to close. If the
   // client allows the change it should delete the window.
   RequestClose(uint32 window_id);
 
   // See description of WindowManager for details.
   GetWindowManager(associated WindowManager& internal);
 };
 
 // Mus provides this interface as a way for clients to connect and obtain a
 // WindowTree handle with a supplied WindowTreeClient handle. The
 // WindowTreeClient has no roots, use NewTopLevelWindow() to create one.
 interface WindowTreeFactory {
   CreateWindowTree(WindowTree& tree_request, WindowTreeClient client);
 };