[SyncFS] Make MetadataDatabase operations synchronous

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 321 matching lines @@
 }
 
 void SyncWorker::AddObserver(Observer* observer) {
   observers_.AddObserver(observer);
 }
 
 void SyncWorker::DoDisableApp(const std::string& app_id,
                               const SyncStatusCallback& callback) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 
-  if (GetMetadataDatabase()) {
-    GetMetadataDatabase()->DisableApp(app_id, callback);
-  } else {
+  if (!GetMetadataDatabase()) {
     callback.Run(SYNC_STATUS_OK);
+    return;
   }
+
+  SyncStatusCode status = GetMetadataDatabase()->DisableApp(app_id);
+  callback.Run(status);
 }
 
 void SyncWorker::DoEnableApp(const std::string& app_id,
                              const SyncStatusCallback& callback) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 
-  if (GetMetadataDatabase()) {
-    GetMetadataDatabase()->EnableApp(app_id, callback);
-  } else {
+  if (!GetMetadataDatabase()) {
     callback.Run(SYNC_STATUS_OK);
+    return;
   }
+
+  SyncStatusCode status = GetMetadataDatabase()->EnableApp(app_id);
+  callback.Run(status);
 }
 
 void SyncWorker::PostInitializeTask() {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
   DCHECK(!GetMetadataDatabase());
 
   // This initializer task may not run if MetadataDatabase in context_ is
   // already initialized when it runs.
   SyncEngineInitializer* initializer =
       new SyncEngineInitializer(context_.get(),
@@ skipping 343 matching lines @@
   return context_->GetDriveUploader();
 }
 
 MetadataDatabase* SyncWorker::GetMetadataDatabase() {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
   return context_->GetMetadataDatabase();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system