AcceleratorProvider: Make GetAcceleratorForCommandId const.

ash/common/system/web_notification/web_notification_tray.h

 // Copyright (c) 2012 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 ASH_COMMON_SYSTEM_WEB_NOTIFICATION_WEB_NOTIFICATION_TRAY_H_
 #define ASH_COMMON_SYSTEM_WEB_NOTIFICATION_WEB_NOTIFICATION_TRAY_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 105 matching lines @@
   bool ShowPopups() override;
   void HidePopups() override;
   bool ShowNotifierSettings() override;
   bool IsContextMenuEnabled() const override;
   message_center::MessageCenterTray* GetMessageCenterTray() override;
 
   // Overridden from SimpleMenuModel::Delegate.
   bool IsCommandIdChecked(int command_id) const override;
   bool IsCommandIdEnabled(int command_id) const override;
   bool GetAcceleratorForCommandId(int command_id,
-                                  ui::Accelerator* accelerator) override;
+                                  ui::Accelerator* accelerator) const override;
   void ExecuteCommand(int command_id, int event_flags) override;
 
   message_center::MessageCenter* message_center() const;
 
  private:
   friend class WebNotificationTrayTest;
 
   FRIEND_TEST_ALL_PREFIXES(WebNotificationTrayTest, WebNotifications);
   FRIEND_TEST_ALL_PREFIXES(WebNotificationTrayTest, WebNotificationPopupBubble);
   FRIEND_TEST_ALL_PREFIXES(WebNotificationTrayTest,
@@ skipping 53 matching lines @@
   bool should_block_shelf_auto_hide_;
 
   std::unique_ptr<AshPopupAlignmentDelegate> popup_alignment_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(WebNotificationTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_WEB_NOTIFICATION_WEB_NOTIFICATION_TRAY_H_