[SyncFS] Make routines using metadata database async

chrome/browser/sync_file_system/drive_backend/sync_engine.h

 // 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.
 
 #ifndef CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_ENGINE_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_ENGINE_H_
 
 #include <set>
 #include <string>
 
@@ skipping 103 matching lines @@
   // drive::DriveServiceObserver overrides.
   virtual void OnReadyToSendRequests() OVERRIDE;
   virtual void OnRefreshTokenInvalid() OVERRIDE;
 
   // net::NetworkChangeNotifier::NetworkChangeObserver overrides.
   virtual void OnNetworkChanged(
       net::NetworkChangeNotifier::ConnectionType type) OVERRIDE;
 
   drive::DriveServiceInterface* GetDriveService();
   drive::DriveUploaderInterface* GetDriveUploader();
-  MetadataDatabase* GetMetadataDatabase();
+
+  // NOTICE: Basically, metadata database runs on |worker_task_runner_|.
+  // Handling it through GetMetadataDatabaseForTesting() in the main thread
+  // may bring race condition.

[tzik, 2014/05/29 02:31:09]

I believe we should convert SyncEngineTest to SyncWorkerTest, which test
SyncWorker directly instead of SyncEngine.
Then, these *ForTesting function should be eventually removed.
Could you leave TODO for it?

[peria, 2014/05/29 03:11:46]

I filed a bug crbug.com/378621.  How about leaving this comment as-is until the
test migration is done?

+  MetadataDatabase* GetMetadataDatabaseForTesting();
   SyncTaskManager* GetSyncTaskManagerForTesting();
 
   void OnPendingFileListUpdated(int item_count);
   void OnFileStatusChanged(const fileapi::FileSystemURL& url,
                            SyncFileStatus file_status,
                            SyncAction sync_action,
                            SyncDirection direction);
   void UpdateServiceState(RemoteServiceState state,
                           const std::string& description);
+  void DidPromoteDemotedChanges(size_t num_trackers);
 
  private:
   class WorkerObserver;
 
   friend class DriveBackendSyncTest;
   friend class SyncEngineTest;
 
   SyncEngine(scoped_ptr<drive::DriveServiceInterface> drive_service,
              scoped_ptr<drive::DriveUploaderInterface> drive_uploader,
              base::SequencedTaskRunner* worker_task_runner,
              drive::DriveNotificationManager* notification_manager,
              ExtensionServiceInterface* extension_service,
              SigninManagerBase* signin_manager);
 
-  void UpdateRegisteredApps();
+  void UpdateRegisteredAppsForTesting();
 
   scoped_ptr<drive::DriveServiceInterface> drive_service_;
   scoped_ptr<DriveServiceWrapper> drive_service_wrapper_;
   scoped_ptr<drive::DriveUploaderInterface> drive_uploader_;
   scoped_ptr<DriveUploaderWrapper> drive_uploader_wrapper_;
   RemoteChangeProcessor* remote_change_processor_;
   scoped_ptr<RemoteChangeProcessorWrapper> remote_change_processor_wrapper_;
 
   scoped_ptr<RemoteChangeProcessorOnWorker> remote_change_processor_on_worker_;
 
@@ skipping 15 matching lines @@
   scoped_refptr<base::SequencedTaskRunner> worker_task_runner_;
 
   base::WeakPtrFactory<SyncEngine> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(SyncEngine);
 };
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_ENGINE_H_