Revert "chromeos: Move files in //ash/common to //ash, part 1"

ash/system/session/logout_button_observer.h

-// Copyright 2014 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_SESSION_LOGOUT_BUTTON_OBSERVER_H_
-#define ASH_SYSTEM_SESSION_LOGOUT_BUTTON_OBSERVER_H_
-
-#include "ash/ash_export.h"
-#include "base/time/time.h"
-
-namespace ash {
-
-class ASH_EXPORT LogoutButtonObserver {
- public:
-  virtual ~LogoutButtonObserver() {}
-
-  // Called when the value of the kShowLogoutButtonInTray pref changes, which
-  // determines whether a logout button should be shown in the system tray
-  // during a session.
-  virtual void OnShowLogoutButtonInTrayChanged(bool show) = 0;
-
-  // Called when the value of the kLogoutDialogDurationMs pref changes.
-  // |duration| is the duration for which the logout confirmation dialog is
-  // shown after the user has pressed the logout button.
-  virtual void OnLogoutDialogDurationChanged(base::TimeDelta duration) = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_SYSTEM_SESSION_LOGOUT_BUTTON_OBSERVER_H_