[Sync] Convert NonBlockingDataTypeController to be single-thread.

components/sync/driver/fake_sync_client.cc

 // Copyright 2015 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/driver/fake_sync_client.h"
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
 #include "components/sync/base/extensions_activity.h"
 #include "components/sync/driver/fake_sync_service.h"
@@ skipping 78 matching lines @@
 
 sync_sessions::SyncSessionsClient* FakeSyncClient::GetSyncSessionsClient() {
   return nullptr;
 }
 
 base::WeakPtr<syncer::SyncableService>
 FakeSyncClient::GetSyncableServiceForType(syncer::ModelType type) {
   return base::WeakPtr<syncer::SyncableService>();
 }
 
-syncer_v2::ModelTypeService* FakeSyncClient::GetModelTypeServiceForType(
-    syncer::ModelType type) {
-  return model_type_service_;
+base::WeakPtr<syncer_v2::ModelTypeService>
+FakeSyncClient::GetModelTypeServiceForType(syncer::ModelType type) {
+  return model_type_service_->AsWeakPtr();
 }
 
 scoped_refptr<syncer::ModelSafeWorker>
 FakeSyncClient::CreateModelWorkerForGroup(
     syncer::ModelSafeGroup group,
     syncer::WorkerLoopDestructionObserver* observer) {
   return scoped_refptr<syncer::ModelSafeWorker>();
 }
 
 SyncApiComponentFactory* FakeSyncClient::GetSyncApiComponentFactory() {
   return factory_;
 }
 
 void FakeSyncClient::SetModelTypeService(
     syncer_v2::ModelTypeService* model_type_service) {
   model_type_service_ = model_type_service;
 }
 
 }  // namespace sync_driver