Use OnceCallback on Mojo interfaces in //ash

ash/system/locale/locale_notification_controller.h

 // 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.
 
 #ifndef ASH_SYSTEM_LOCALE_LOCALE_NOTIFICATION_CONTROLLER_H_
 #define ASH_SYSTEM_LOCALE_LOCALE_NOTIFICATION_CONTROLLER_H_
 
 #include <string>
 
 #include "ash/public/interfaces/locale.mojom.h"
@@ skipping 11 matching lines @@
 
   // Binds the mojom::LocaleNotificationController interface request to this
   // object.
   void BindRequest(mojom::LocaleNotificationControllerRequest request);
 
  private:
   // Overridden from mojom::LocaleNotificationController:
   void OnLocaleChanged(const std::string& cur_locale,
                        const std::string& from_locale,
                        const std::string& to_locale,
-                       const OnLocaleChangedCallback& callback) override;
+                       OnLocaleChangedCallback callback) override;
 
   std::string cur_locale_;
   std::string from_locale_;
   std::string to_locale_;
 
   // Bindings for the LocaleNotificationController interface.
   mojo::BindingSet<mojom::LocaleNotificationController> bindings_;
 
   DISALLOW_COPY_AND_ASSIGN(LocaleNotificationController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_LOCALE_LOCALE_NOTIFICATION_CONTROLLER_H_