[SyncFS] Make MetadataDatabase operations synchronous

chrome/browser/sync_file_system/drive_backend/register_app_task.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/register_app_task.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "chrome/browser/drive/drive_api_util.h"
 #include "chrome/browser/drive/drive_service_interface.h"
@@ skipping 150 matching lines @@
   if (!oldest_tracker)
     return false;
 
   *candidate = *oldest_tracker;
   return true;
 }
 
 void RegisterAppTask::RegisterAppIntoDatabase(
     const FileTracker& tracker,
     const SyncStatusCallback& callback) {
-  metadata_database()->RegisterApp(
-      app_id_, tracker.file_id(), callback);
+  SyncStatusCode status =
+      metadata_database()->RegisterApp(app_id_, tracker.file_id());
+  callback.Run(status);
 }
 
 MetadataDatabase* RegisterAppTask::metadata_database() {
   return sync_context_->GetMetadataDatabase();
 }
 
 drive::DriveServiceInterface* RegisterAppTask::drive_service() {
   return sync_context_->GetDriveService();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system