[SyncFS] Make task invocation in SyncTaskRunner async

chrome/browser/sync_file_system/drive_backend/sync_worker.cc

 // Copyright 2014 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 "chrome/browser/sync_file_system/drive_backend/sync_worker.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "chrome/browser/drive/drive_service_interface.h"
@@ skipping 52 matching lines @@
   observers_.Clear();
 }
 
 void SyncWorker::Initialize(scoped_ptr<SyncEngineContext> context) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
   DCHECK(!task_manager_);
 
   context_ = context.Pass();
 
   task_manager_.reset(new SyncTaskManager(
-      weak_ptr_factory_.GetWeakPtr(), 0 /* maximum_background_task */));
+      weak_ptr_factory_.GetWeakPtr(), 0 /* maximum_background_task */,
+      context_->GetWorkerTaskRunner()));
   task_manager_->Initialize(SYNC_STATUS_OK);
 
   PostInitializeTask();
 
   net::NetworkChangeNotifier::ConnectionType type =
       net::NetworkChangeNotifier::GetConnectionType();
   network_available_ =
       type != net::NetworkChangeNotifier::CONNECTION_NONE;
 }
 
@@ skipping 657 matching lines @@
             "Service state changed: %d->%d: %s",
             old_state, GetCurrentState(), description.c_str());
 
   FOR_EACH_OBSERVER(
       Observer, observers_,
       UpdateServiceState(GetCurrentState(), description));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system