[SyncFS] Remove using MessageLoop in worker thread

chrome/browser/sync_file_system/drive_backend/remote_to_local_syncer.cc

 // Copyright 2013 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/remote_to_local_syncer.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/format_macros.h"
 #include "base/location.h"
@@ skipping 95 matching lines @@
           dirty_tracker_.get())) {
     util::Log(logging::LOG_VERBOSE, FROM_HERE,
               "[Remote -> Local] Start: tracker_id=%" PRId64,
               dirty_tracker_->tracker_id());
     ResolveRemoteChange(wrapped_callback);
     return;
   }
 
   util::Log(logging::LOG_VERBOSE, FROM_HERE,
             "[Remote -> Local] Nothing to do.");
-  base::MessageLoopProxy::current()->PostTask(
+  sync_context_->GetWorkerTaskRunner()->PostTask(
       FROM_HERE,
       base::Bind(callback, SYNC_STATUS_NO_CHANGE_TO_SYNC));
 }
 
 void RemoteToLocalSyncer::ResolveRemoteChange(
     const SyncStatusCallback& callback) {
   DCHECK(dirty_tracker_);
   remote_metadata_ = GetFileMetadata(
       metadata_database(), dirty_tracker_->file_id());
 
@@ skipping 635 matching lines @@
   return sync_context_->GetMetadataDatabase();
 }
 
 RemoteChangeProcessor* RemoteToLocalSyncer::remote_change_processor() {
   DCHECK(sync_context_->GetRemoteChangeProcessor());
   return sync_context_->GetRemoteChangeProcessor();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system