mash: Migrate locale observer and notification to common.

ash/system/locale/locale_observer.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_SYSTEM_LOCALE_LOCALE_OBSERVER_H_
-#define ASH_SYSTEM_LOCALE_LOCALE_OBSERVER_H_
-
-#include "ash/ash_export.h"
-
-namespace ash {
-
-class ASH_EXPORT LocaleObserver {
- public:
-  class Delegate {
-   public:
-    virtual ~Delegate() {}
-
-    virtual void AcceptLocaleChange() = 0;
-    virtual void RevertLocaleChange() = 0;
-  };
-
-  virtual ~LocaleObserver() {}
-
-  virtual void OnLocaleChanged(Delegate* delegate,
-                               const std::string& cur_locale,
-                               const std::string& from_locale,
-                               const std::string& to_locale) = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_SYSTEM_LOCALE_LOCALE_OBSERVER_H_