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

components/sync/engine/passive_model_worker.cc

 // 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.
 
 #include "components/sync/engine/passive_model_worker.h"
 
-#include <utility>
+#include "base/callback.h"
 
 namespace syncer {
 
 PassiveModelWorker::PassiveModelWorker() = default;
 
 PassiveModelWorker::~PassiveModelWorker() {}
 
-void PassiveModelWorker::ScheduleWork(base::OnceClosure work) {
-  std::move(work).Run();
+SyncerError PassiveModelWorker::DoWorkAndWaitUntilDoneImpl(
+    const WorkCallback& work) {
+  // Simply do the work on the current thread.
+  return work.Run();
 }
 
 ModelSafeGroup PassiveModelWorker::GetModelSafeGroup() {
   return GROUP_PASSIVE;
 }
 
 bool PassiveModelWorker::IsOnModelThread() {
   // Passive types are checked by SyncBackendRegistrar.
   NOTREACHED();
   return false;
 }
 
 }  // namespace syncer