components: Cleanup class/struct fwd declarations

components/sync/engine_impl/model_type_worker.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 COMPONENTS_SYNC_ENGINE_IMPL_MODEL_TYPE_WORKER_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_MODEL_TYPE_WORKER_H_
 
 #include <stddef.h>
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "components/sync/base/cryptographer.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/engine/commit_queue.h"
 #include "components/sync/engine/non_blocking_sync_common.h"
 #include "components/sync/engine/sync_encryption_handler.h"
 #include "components/sync/engine_impl/commit_contributor.h"
 #include "components/sync/engine_impl/cycle/data_type_debug_info_emitter.h"
 #include "components/sync/engine_impl/nudge_handler.h"
 #include "components/sync/engine_impl/update_handler.h"
 #include "components/sync/protocol/model_type_state.pb.h"
 #include "components/sync/protocol/sync.pb.h"
 
-namespace base {
-class SingleThreadTaskRunner;
-}
-
 namespace syncer {
 
 class ModelTypeProcessor;
 class WorkerEntityTracker;
 
 // A smart cache for sync types that use message passing (rather than
 // transactions and the syncable::Directory) to communicate with the sync
 // thread.
 //
 // When the non-blocking sync type wants to talk with the sync server, it will
@@ skipping 161 matching lines @@
   // Whether there are outstanding encrypted updates in |entities_|.
   bool has_encrypted_updates_ = false;
 
   base::ThreadChecker thread_checker_;
   base::WeakPtrFactory<ModelTypeWorker> weak_ptr_factory_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_MODEL_TYPE_WORKER_H_