mash: Use the new mus drag and drop API to get drag working in mash.

services/ui/public/cpp/window_tree_client.h

 // 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.
 
 #ifndef SERVICES_UI_PUBLIC_CPP_WINDOW_TREE_CLIENT_H_
 #define SERVICES_UI_PUBLIC_CPP_WINDOW_TREE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 160 matching lines @@
   gfx::Point GetCursorScreenPoint();
 
   // See description in window_tree.mojom. When an existing pointer watcher is
   // updated or cleared then any future events from the server for that watcher
   // will be ignored.
   void StartPointerWatcher(bool want_moves);
   void StopPointerWatcher();
 
   void PerformDragDrop(
       Window* window,
-      int drag_pointer,
       const std::map<std::string, std::vector<uint8_t>>& drag_data,
       int drag_operation,
       const gfx::Point& cursor_location,
       const SkBitmap& bitmap,
       const base::Callback<void(bool, uint32_t)>& callback);
 
   // Cancels a in progress drag drop. (If no drag is in progress, does
   // nothing.)
   void CancelDragDrop(Window* window);
 
@@ skipping 287 matching lines @@
   std::set<Id> drag_entered_windows_;
 
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);
 };
 
 }  // namespace ui
 
 #endif  // SERVICES_UI_PUBLIC_CPP_WINDOW_TREE_CLIENT_H_