[ash] Create applist button's context menu in its ShelfItemDelegate

ash/shelf/app_list_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/shelf/app_list_shelf_item_delegate.h"
 
 #include "ash/shelf/shelf_model.h"
 #include "ash/shell.h"
+#include "ash/shell_delegate.h"
 #include "grit/ash_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 
 namespace ash {
 namespace internal {
 
 AppListShelfItemDelegate::AppListShelfItemDelegate() {
   LauncherItem app_list;
   app_list.type = TYPE_APP_LIST;
   Shell::GetInstance()->shelf_model()->Add(app_list);
@@ skipping 12 matching lines @@
 base::string16 AppListShelfItemDelegate::GetTitle() {
   ShelfModel* model = Shell::GetInstance()->shelf_model();
   DCHECK(model);
   return model->status() == ShelfModel::STATUS_LOADING ?
       l10n_util::GetStringUTF16(IDS_AURA_APP_LIST_SYNCING_TITLE) :
       l10n_util::GetStringUTF16(IDS_AURA_APP_LIST_TITLE);
 }
 
 ui::MenuModel* AppListShelfItemDelegate::CreateContextMenu(
     aura::Window* root_window) {
-  return NULL;
+  return Shell::GetInstance()->delegate()->CreateContextMenu(root_window);
 }
 
 ShelfMenuModel* AppListShelfItemDelegate::CreateApplicationMenu(
     int event_flags) {
   // AppList does not show an application menu.
   return NULL;
 }
 
 bool AppListShelfItemDelegate::IsDraggable() {
   return false;
 }
 
 bool AppListShelfItemDelegate::ShouldShowTooltip() {
   return true;
 }
 
 }  // namespace internal
 }  // namespace ash