Do not observe MessageLoop destruction from ModelSafeWorker.

components/sync/driver/fake_sync_client.h

 // 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.
 
 #ifndef COMPONENTS_SYNC_DRIVER_FAKE_SYNC_CLIENT_H_
 #define COMPONENTS_SYNC_DRIVER_FAKE_SYNC_CLIENT_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 24 matching lines @@
   autofill::PersonalDataManager* GetPersonalDataManager() override;
   BookmarkUndoService* GetBookmarkUndoServiceIfExists() override;
   invalidation::InvalidationService* GetInvalidationService() override;
   scoped_refptr<ExtensionsActivity> GetExtensionsActivity() override;
   sync_sessions::SyncSessionsClient* GetSyncSessionsClient() override;
   base::WeakPtr<SyncableService> GetSyncableServiceForType(
       ModelType type) override;
   base::WeakPtr<ModelTypeSyncBridge> GetSyncBridgeForModelType(
       ModelType type) override;
   scoped_refptr<ModelSafeWorker> CreateModelWorkerForGroup(
-      ModelSafeGroup group,
-      WorkerLoopDestructionObserver* observer) override;
+      ModelSafeGroup group) override;
   SyncApiComponentFactory* GetSyncApiComponentFactory() override;
 
   void SetModelTypeSyncBridge(ModelTypeSyncBridge* bridge);
 
  private:
   sync_preferences::TestingPrefServiceSyncable pref_service_;
   ModelTypeSyncBridge* bridge_;
   SyncApiComponentFactory* factory_;
   std::unique_ptr<FakeSyncService> sync_service_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeSyncClient);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_FAKE_SYNC_CLIENT_H_