Replace more ObserverList with base::ObserverList.

components/history/core/browser/history_backend.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 COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 
 #include <set>
 #include <string>
 #include <utility>
@@ skipping 804 matching lines @@
   scoped_ptr<HistoryBackendHelper> supports_user_data_helper_;
 
   // Used to manage syncing of the typed urls datatype. This will be null before
   // Init is called.
   scoped_ptr<TypedUrlSyncableService> typed_url_syncable_service_;
 
   // Listens for the system being under memory pressure.
   scoped_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
   // List of observers
-  ObserverList<HistoryBackendObserver> observers_;
+  base::ObserverList<HistoryBackendObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_