Replace more ObserverList with base::ObserverList.

ash/shelf/shelf_model.h

 // Copyright 2013 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_SHELF_SHELF_MODEL_H_
 #define ASH_SHELF_SHELF_MODEL_H_
 
 #include "ash/ash_export.h"
 #include "ash/shelf/shelf_item_types.h"
 #include "base/basictypes.h"
@@ skipping 73 matching lines @@
   // Makes sure |index| is in line with the type-based order of items. If that
   // is not the case, adjusts index by shifting it to the valid range and
   // returns the new value.
   int ValidateInsertionIndex(ShelfItemType type, int index) const;
 
   // ID assigned to the next item.
   ShelfID next_id_;
 
   ShelfItems items_;
   Status status_;
-  ObserverList<ShelfModelObserver> observers_;
+  base::ObserverList<ShelfModelObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfModel);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_MODEL_H_