mus drag and drop: Add API to let the client cancel the drag.

services/ui/ws/window_manager_state.h

 // Copyright 2016 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.
 
 #ifndef SERVICES_UI_WS_WINDOW_MANAGER_STATE_H_
 #define SERVICES_UI_WS_WINDOW_MANAGER_STATE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 53 matching lines @@
   void ReleaseCaptureBlockedByModalWindow(const ServerWindow* modal_window);
   void ReleaseCaptureBlockedByAnyModalWindow();
 
   void SetDragDropSourceWindow(
       DragSource* drag_source,
       ServerWindow* window,
       DragTargetConnection* source_connection,
       int32_t drag_pointer,
       mojo::Map<mojo::String, mojo::Array<uint8_t>> drag_data,
       uint32_t drag_operation);
+  void CancelDragDrop();
   void EndDragDrop();
 
   void AddSystemModalWindow(ServerWindow* window);
 
   // Returns the ServerWindow corresponding to an orphaned root with the
   // specified id. See |orphaned_window_manager_display_roots_| for details on
   // what on orphaned root is.
   ServerWindow* GetOrphanedRootWithId(const WindowId& id);
 
   // TODO(sky): EventDispatcher is really an implementation detail and should
@@ skipping 182 matching lines @@
 
   base::WeakPtrFactory<WindowManagerState> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowManagerState);
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_WINDOW_MANAGER_STATE_H_