Moves ShellObserver to ash/common

ash/system/chromeos/rotation/tray_rotation_lock.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_CHROMEOS_ROTATION_TRAY_ROTATION_LOCK_H_
 #define ASH_SYSTEM_CHROMEOS_ROTATION_TRAY_ROTATION_LOCK_H_
 
+#include "ash/common/shell_observer.h"
 #include "ash/display/screen_orientation_controller_chromeos.h"
-#include "ash/shell_observer.h"
 #include "ash/system/tray/tray_image_item.h"
 #include "base/macros.h"
 
 namespace ash {
 
 namespace tray {
 class RotationLockDefaultView;
 }  // namespace tray
 
 // TrayRotationLock is a provider of views for the SystemTray. Both a tray view
@@ skipping 48 matching lines @@
 
   // True while added as a ShellObserver.
   bool observing_shell_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayRotationLock);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_ROTATION_TRAY_ROTATION_LOCK_H_