Replace more ObserverList with base::ObserverList.

sync/sessions/model_type_registry.h

 // Copyright 2014 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 SYNC_ENGINE_MODEL_TYPE_REGISTRY_H_
 #define SYNC_ENGINE_MODEL_TYPE_REGISTRY_H_
 
 #include <map>
 
 #include "base/basictypes.h"
@@ skipping 132 matching lines @@
 
   // The set of enabled directory types.
   ModelTypeSet enabled_directory_types_;
 
   // The set of observers of per-type debug info.
   //
   // Each of the DirectoryTypeDebugInfoEmitters needs such a list.  There's
   // a lot of them, and their lifetimes are unpredictable, so it makes the
   // book-keeping easier if we just store the list here.  That way it's
   // guaranteed to live as long as this sync backend.
-  ObserverList<TypeDebugInfoObserver> type_debug_info_observers_;
+  base::ObserverList<TypeDebugInfoObserver> type_debug_info_observers_;
 
   base::WeakPtrFactory<ModelTypeRegistry> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ModelTypeRegistry);
 };
 
 }  // namespace syncer
 
 #endif // SYNC_ENGINE_MODEL_TYPE_REGISTRY_H_