[SyncFS] Add completion callback to PromoteDemotedChanges (1/3)

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 216 matching lines @@
     return;
 
   FOR_EACH_OBSERVER(
       Observer,
       observers_,
       UpdateServiceState(
           GetCurrentState(),
           enabled ? "Sync is enabled" : "Sync is disabled"));
 }
 
-void SyncWorker::PromoteDemotedChanges() {
+void SyncWorker::PromoteDemotedChanges(const base::Closure& callback) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 
   MetadataDatabase* metadata_db = GetMetadataDatabase();
   if (metadata_db && metadata_db->HasLowPriorityDirtyTracker()) {
     metadata_db->PromoteLowerPriorityTrackersToNormal();
     FOR_EACH_OBSERVER(
         Observer,
         observers_,
         OnPendingFileListUpdated(metadata_db->CountDirtyTracker()));
   }
+  callback.Run();
 }
 
 void SyncWorker::ApplyLocalChange(
     const FileChange& local_change,
     const base::FilePath& local_path,
     const SyncFileMetadata& local_metadata,
     const fileapi::FileSystemURL& url,
     const SyncStatusCallback& callback) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 
@@ skipping 480 matching lines @@
   return context_->GetDriveUploader();
 }
 
 MetadataDatabase* SyncWorker::GetMetadataDatabase() {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
   return context_->GetMetadataDatabase();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system