mash: Cleanup ash shelf application menu code.

ash/shell/window_watcher_shelf_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/shell/window_watcher_shelf_item_delegate.h"
 
 #include "ash/shell/window_watcher.h"
 #include "ash/wm/window_util.h"
 #include "ui/aura/window.h"
 
@@ skipping 13 matching lines @@
 ShelfItemDelegate::PerformedAction WindowWatcherShelfItemDelegate::ItemSelected(
     const ui::Event& event) {
   aura::Window* window = watcher_->GetWindowByID(id_);
   if (window->type() == ui::wm::WINDOW_TYPE_PANEL)
     wm::MoveWindowToEventRoot(window, event);
   window->Show();
   wm::ActivateWindow(window);
   return kExistingWindowActivated;
 }
 
-ui::SimpleMenuModel* WindowWatcherShelfItemDelegate::CreateApplicationMenu(
+ShelfAppMenuItemList WindowWatcherShelfItemDelegate::GetAppMenuItems(
     int event_flags) {
-  return nullptr;
+  // Return an empty item list to avoid showing an application menu.
+  return ShelfAppMenuItemList();
 }
 
 void WindowWatcherShelfItemDelegate::Close() {}
 
 }  // namespace shell
 }  // namespace ash