[Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

components/sync/test/engine/fake_model_worker.h

 // Copyright (c) 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_TEST_ENGINE_FAKE_MODEL_WORKER_H_
 #define COMPONENTS_SYNC_TEST_ENGINE_FAKE_MODEL_WORKER_H_
 
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "components/sync/base/syncer_error.h"
 #include "components/sync/engine/model_safe_worker.h"
 
 namespace syncer {
 
 // Fake implementation of ModelSafeWorker that does work on the
 // current thread regardless of the group.
 class FakeModelWorker : public ModelSafeWorker {
  public:
   explicit FakeModelWorker(ModelSafeGroup group);
 
   // ModelSafeWorker implementation.
   ModelSafeGroup GetModelSafeGroup() override;
   bool IsOnModelThread() override;
 
- protected:
-  SyncerError DoWorkAndWaitUntilDoneImpl(const WorkCallback& work) override;
-
  private:
   ~FakeModelWorker() override;
 
+  void ScheduleWork(base::OnceClosure work) override;
+
   const ModelSafeGroup group_;
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeModelWorker);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_TEST_ENGINE_FAKE_MODEL_WORKER_H_