mash: Cleanup ash shelf application menu code.

ash/common/shelf/shelf_window_watcher_item_delegate.cc

 // Copyright 2013 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.
 
 #include "ash/common/shelf/shelf_window_watcher_item_delegate.h"
 
 #include "ash/common/shelf/shelf_controller.h"
 #include "ash/common/shelf/shelf_model.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm_shell.h"
@@ skipping 37 matching lines @@
       window_->Animate(::wm::WINDOW_ANIMATION_TYPE_BOUNCE);
       return kNoAction;
     }
     window_->Minimize();
     return kExistingWindowMinimized;
   }
   window_->Activate();
   return kExistingWindowActivated;
 }
 
-ui::SimpleMenuModel* ShelfWindowWatcherItemDelegate::CreateApplicationMenu(
+ShelfAppMenuItemList ShelfWindowWatcherItemDelegate::GetAppMenuItems(
     int event_flags) {
-  return nullptr;
+  // Return an empty item list to avoid showing an application menu.
+  return ShelfAppMenuItemList();
 }
 
 void ShelfWindowWatcherItemDelegate::Close() {
   window_->CloseWidget();
 }
 
 }  // namespace ash