[Sync] Move sync's ModelSafeWorker implementations to engine/.

components/sync/driver/glue/browser_thread_model_worker.h

-// Copyright 2012 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_BROWSER_THREAD_MODEL_WORKER_H_
-#define COMPONENTS_SYNC_DRIVER_GLUE_BROWSER_THREAD_MODEL_WORKER_H_
-
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/single_thread_task_runner.h"
-#include "components/sync/base/scoped_event_signal.h"
-#include "components/sync/base/syncer_error.h"
-#include "components/sync/engine/model_safe_worker.h"
-
-namespace syncer {
-
-// A ModelSafeWorker for models that accept requests from the
-// syncapi that need to be fulfilled on a browser thread, for example
-// autofill on the DB thread.
-// TODO(sync): Try to generalize other ModelWorkers (e.g. history, etc).
-class BrowserThreadModelWorker : public ModelSafeWorker {
- public:
-  BrowserThreadModelWorker(
-      const scoped_refptr<base::SingleThreadTaskRunner>& runner,
-      ModelSafeGroup group);
-
-  // ModelSafeWorker implementation.
-  ModelSafeGroup GetModelSafeGroup() override;
-  bool IsOnModelThread() override;
-
- protected:
-  ~BrowserThreadModelWorker() override;
-
-  SyncerError DoWorkAndWaitUntilDoneImpl(const WorkCallback& work) override;
-
-  void CallDoWorkAndSignalTask(const WorkCallback& work,
-                               syncer::ScopedEventSignal scoped_event_signal,
-                               SyncerError* error);
-
- private:
-  scoped_refptr<base::SingleThreadTaskRunner> runner_;
-  ModelSafeGroup group_;
-
-  DISALLOW_COPY_AND_ASSIGN(BrowserThreadModelWorker);
-};
-
-}  // namespace syncer
-
-#endif  // COMPONENTS_SYNC_DRIVER_GLUE_BROWSER_THREAD_MODEL_WORKER_H_