[SyncFS] Run RemoteToLocalSyncer as a background task

chrome/browser/sync_file_system/drive_backend/local_to_remote_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/local_to_remote_syncer.h"
 
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
@@ skipping 272 matching lines @@
   // ContinueAsBackgroundTask(), so we need to make sure other tasks didn't
   // affect to the current LocalToRemoteSyncer task.
   //
   // - For RemoteToLocalSyncer, it doesn't actually run beyond
   //   PrepareForProcessRemoteChange() since it should be blocked in
   //   LocalFileSyncService.
   // - For ListChangesTask, it may update FileMetatada together with |change_id|
   //   and may delete FileTracker.  So, ensure |change_id| is not changed and
   //   check if FileTracker still exists.
   // - For UninstallAppTask, it may also delete FileMetadata and FileTracker.
-  //   And also, check if FileTracker still exists.
+  //   Check if FileTracker still exists.
   // - Others, SyncEngineInitializer and RegisterAppTask doesn't affect to
   //   LocalToRemoteSyncer.
   if (remote_file_tracker_) {
     int64 latest_change_id = 0;
     if (!GetKnownChangeID(metadata_database(),
                           remote_file_tracker_->file_id(),
                           &latest_change_id) ||
         latest_change_id > remote_file_change_id_) {
       SyncCompleted(token.Pass(), SYNC_STATUS_RETRY);
       return;
@@ skipping 352 matching lines @@
     NOTREACHED();
     SyncCompleted(token.Pass(), SYNC_STATUS_FAILED);
     return;
   }
 
   status = metadata_database()->ReplaceActiveTrackerWithNewResource(
       remote_parent_folder_tracker_->tracker_id(), *entry);
   SyncCompleted(token.Pass(), status);
 }
 
-void LocalToRemoteSyncer::CreateRemoteFolder(
-    scoped_ptr<SyncTaskToken> token) {
+void LocalToRemoteSyncer::CreateRemoteFolder(scoped_ptr<SyncTaskToken> token) {
   DCHECK(remote_parent_folder_tracker_);
 
   base::FilePath title = storage::VirtualPath::BaseName(target_path_);
   sync_action_ = SYNC_ACTION_ADDED;
 
   DCHECK(!folder_creator_);
   folder_creator_.reset(new FolderCreator(
       drive_service(), metadata_database(),
       remote_parent_folder_tracker_->file_id(),
       title.AsUTF8Unsafe()));
@@ skipping 68 matching lines @@
   set_used_network(true);
   return sync_context_->GetDriveUploader();
 }
 
 MetadataDatabase* LocalToRemoteSyncer::metadata_database() {
   return sync_context_->GetMetadataDatabase();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system