Replace more ObserverList with base::ObserverList.

ui/app_list/search/history_data.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 UI_APP_LIST_SEARCH_HISTORY_DATA_H_
 #define UI_APP_LIST_SEARCH_HISTORY_DATA_H_
 
 #include <deque>
 #include <map>
 #include <string>
@@ skipping 64 matching lines @@
  private:
   // Invoked from |store| with loaded data.
   void OnStoreLoaded(scoped_ptr<Associations> loaded_data);
 
   // Trims the data to keep the most recent |max_primary_| queries.
   void TrimEntries();
 
   HistoryDataStore* store_;  // Not owned.
   const size_t max_primary_;
   const size_t max_secondary_;
-  ObserverList<HistoryDataObserver, true> observers_;
+  base::ObserverList<HistoryDataObserver, true> observers_;
 
   Associations associations_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryData);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SEARCH_HISTORY_DATA_H_