Do not observe MessageLoop destruction from ModelSafeWorker.

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/base/sync_prefs.h"
@@ skipping 82 matching lines @@
     ModelType type) {
   return base::WeakPtr<SyncableService>();
 }
 
 base::WeakPtr<ModelTypeSyncBridge> FakeSyncClient::GetSyncBridgeForModelType(
     ModelType type) {
   return bridge_->AsWeakPtr();
 }
 
 scoped_refptr<ModelSafeWorker> FakeSyncClient::CreateModelWorkerForGroup(
-    ModelSafeGroup group,
-    WorkerLoopDestructionObserver* observer) {
+    ModelSafeGroup group) {
   return scoped_refptr<ModelSafeWorker>();
 }
 
 SyncApiComponentFactory* FakeSyncClient::GetSyncApiComponentFactory() {
   return factory_;
 }
 
 void FakeSyncClient::SetModelTypeSyncBridge(ModelTypeSyncBridge* bridge) {
   bridge_ = bridge;
 }
 
 }  // namespace syncer