Rename the aura_shell namespace to ash

ash/app_list/app_list_item_model_observer.h

 // Copyright (c) 2011 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_APP_LIST_APP_LIST_ITEM_MODEL_OBSERVER_H_
 #define ASH_APP_LIST_APP_LIST_ITEM_MODEL_OBSERVER_H_
 #pragma once
 
 #include "ash/ash_export.h"
 
-namespace aura_shell {
+namespace ash {
 
 class ASH_EXPORT AppListItemModelObserver {
  public:
   // Invoked after app list item's icon is changed.
   virtual void ItemIconChanged() = 0;
 
   // Invoked after app list item's title is changed.
   virtual void ItemTitleChanged() = 0;
 
  protected:
   virtual ~AppListItemModelObserver() {}
 };
 
-}  // namespace aura_shell
+}  // namespace ash
 
 #endif  // ASH_APP_LIST_APP_LIST_ITEM_MODEL_OBSERVER_H_