[SyncFS] Make routines using metadata database async

chrome/browser/sync_file_system/drive_backend/sync_engine.h

Index: chrome/browser/sync_file_system/drive_backend/sync_engine.h
diff --git a/chrome/browser/sync_file_system/drive_backend/sync_engine.h b/chrome/browser/sync_file_system/drive_backend/sync_engine.h
index 45bf4b344f379ca6fd622d7161cf8c0958ba235b..24040a19713b157b26f7107e112280e94ec574dc 100644
--- a/chrome/browser/sync_file_system/drive_backend/sync_engine.h
+++ b/chrome/browser/sync_file_system/drive_backend/sync_engine.h
@@ -121,7 +121,7 @@ class SyncEngine : public RemoteFileSyncService,
 
   drive::DriveServiceInterface* GetDriveService();
   drive::DriveUploaderInterface* GetDriveUploader();
-  MetadataDatabase* GetMetadataDatabase();
+  MetadataDatabase* GetMetadataDatabaseForTesting();
   SyncTaskManager* GetSyncTaskManagerForTesting();
 
   void OnPendingFileListUpdated(int item_count);
@@ -131,6 +131,7 @@ class SyncEngine : public RemoteFileSyncService,
                            SyncDirection direction);
   void UpdateServiceState(RemoteServiceState state,
                           const std::string& description);
+  void DidPromoteDemotedChanges(size_t num_trackers);
 
  private:
   class WorkerObserver;
@@ -145,7 +146,7 @@ class SyncEngine : public RemoteFileSyncService,
              ExtensionServiceInterface* extension_service,
              SigninManagerBase* signin_manager);
 
-  void UpdateRegisteredApps();
+  void UpdateRegisteredAppsForTesting();
 
   scoped_ptr<drive::DriveServiceInterface> drive_service_;
   scoped_ptr<DriveServiceWrapper> drive_service_wrapper_;