components: Cleanup class/struct fwd declarations

components/history/core/browser/typed_url_syncable_service.h

 // Copyright (c) 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 COMPONENTS_HISTORY_CORE_BROWSER_TYPED_URL_SYNCABLE_SERVICE_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_TYPED_URL_SYNCABLE_SERVICE_H_
 
 #include <stdint.h>
 
 #include <set>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/scoped_observer.h"
 #include "base/threading/thread_checker.h"
 #include "components/history/core/browser/history_backend_observer.h"
 #include "components/history/core/browser/history_types.h"
 #include "components/sync/model/sync_change.h"
 #include "components/sync/model/sync_data.h"
 #include "components/sync/model/sync_error.h"
 #include "components/sync/model/sync_error_factory.h"
 #include "components/sync/model/syncable_service.h"
 #include "ui/base/page_transition_types.h"
 
 class GURL;
 
-namespace base {
-class MessageLoop;
-};
-
 namespace sync_pb {
 class TypedUrlSpecifics;
 };
 
 namespace history {
 
 class HistoryBackend;
 class TypedUrlSyncableServiceTest;
 class URLRow;
 
@@ skipping 199 matching lines @@
 
   ScopedObserver<history::HistoryBackend, history::HistoryBackendObserver>
       history_backend_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(TypedUrlSyncableService);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_TYPED_URL_SYNCABLE_SERVICE_H_