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_COMMON_SYSTEM_CHROMEOS_SESSION_LOGOUT_BUTTON_OBSERVER_H_
-#define ASH_COMMON_SYSTEM_CHROMEOS_SESSION_LOGOUT_BUTTON_OBSERVER_H_
+#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_COMMON_SYSTEM_CHROMEOS_SESSION_LOGOUT_BUTTON_OBSERVER_H_
+#endif  // ASH_SYSTEM_SESSION_LOGOUT_BUTTON_OBSERVER_H_