components: Cleanup class/struct fwd declarations

components/sync/driver/glue/sync_backend_host_impl.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 COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_IMPL_H_
 #define COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 16 matching lines @@
 #include "components/sync/driver/glue/sync_backend_host.h"
 #include "components/sync/engine/configure_reason.h"
 #include "components/sync/engine/cycle/sync_cycle_snapshot.h"
 #include "components/sync/engine/cycle/type_debug_info_observer.h"
 #include "components/sync/engine/sync_manager.h"
 #include "components/sync/protocol/encryption.pb.h"
 #include "components/sync/protocol/sync_protocol_error.h"
 
 class GURL;
 
-namespace base {
-class MessageLoop;
-}  // base
-
 namespace invalidation {
 class InvalidationService;
 }  // namespace invalidation
 
 namespace syncer {
 
 class ChangeProcessor;
 class SyncBackendHostCore;
 class SyncBackendRegistrar;
 class SyncClient;
@@ skipping 301 matching lines @@
   bool invalidation_handler_registered_;
 
   base::WeakPtrFactory<SyncBackendHostImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHostImpl);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_IMPL_H_