mash: Migrate some system user files to common.

ash/system/tray/system_tray_notifier.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_TRAY_SYSTEM_TRAY_NOTIFIER_H_
 #define ASH_SYSTEM_TRAY_SYSTEM_TRAY_NOTIFIER_H_
 
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "ash/ash_export.h"
-#include "ash/system/user/user_observer.h"
+#include "ash/common/system/user/user_observer.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 
 #if defined(OS_CHROMEOS)
 #include "ash/system/chromeos/bluetooth/bluetooth_observer.h"
 #include "ash/system/chromeos/enterprise/enterprise_domain_observer.h"
 #include "ash/system/chromeos/network/network_observer.h"
 #include "ash/system/chromeos/network/network_portal_detector_observer.h"
 #include "ash/system/chromeos/screen_security/screen_capture_observer.h"
 #include "ash/system/chromeos/screen_security/screen_share_observer.h"
@@ skipping 90 matching lines @@
   base::ObserverList<ScreenShareObserver> screen_share_observers_;
   base::ObserverList<LastWindowClosedObserver> last_window_closed_observers_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayNotifier);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_SYSTEM_TRAY_NOTIFIER_H_