Moves ShellObserver to ash/common

ash/aura/wm_root_window_controller_aura.h

 // Copyright 2016 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_AURA_WM_ROOT_CONTROLLER_AURA_H_
 #define ASH_AURA_WM_ROOT_CONTROLLER_AURA_H_
 
 #include "ash/ash_export.h"
+#include "ash/common/shell_observer.h"
 #include "ash/common/wm_root_window_controller.h"
-#include "ash/shell_observer.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 
 namespace aura {
 class Window;
 }
 
 namespace ash {
 
 class RootWindowController;
@@ skipping 35 matching lines @@
  private:
   RootWindowController* root_window_controller_;
   base::ObserverList<WmRootWindowControllerObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WmRootWindowControllerAura);
 };
 
 }  // namespace ash
 
 #endif  // ASH_AURA_WM_ROOT_CONTROLLER_AURA_H_