[SyncFS] Make MetadataDatabase operations synchronous

chrome/browser/sync_file_system/drive_backend/uninstall_app_task.cc

Index: chrome/browser/sync_file_system/drive_backend/uninstall_app_task.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/uninstall_app_task.cc b/chrome/browser/sync_file_system/drive_backend/uninstall_app_task.cc
index 74f38f30df6acc54a126480b6bf5ba4087b7cdbf..e97dbf1fe4e791ffdd119de9e99150e4e40d793b 100644
--- a/chrome/browser/sync_file_system/drive_backend/uninstall_app_task.cc
+++ b/chrome/browser/sync_file_system/drive_backend/uninstall_app_task.cc
@@ -41,7 +41,8 @@ void UninstallAppTask::RunExclusive(const SyncStatusCallback& callback) {
   }
 
   if (uninstall_flag_ == RemoteFileSyncService::UNINSTALL_AND_KEEP_REMOTE) {
-    metadata_database()->UnregisterApp(app_id_, callback);
+    SyncStatusCode status = metadata_database()->UnregisterApp(app_id_);
+    callback.Run(status);
     return;
   }
   DCHECK_EQ(RemoteFileSyncService::UNINSTALL_AND_PURGE_REMOTE, uninstall_flag_);
@@ -84,7 +85,8 @@ void UninstallAppTask::DidDeleteAppRoot(const SyncStatusCallback& callback,
     return;
   }
 
-  metadata_database()->UnregisterApp(app_id_, callback);
+  status = metadata_database()->UnregisterApp(app_id_);
+  callback.Run(status);
 }
 
 bool UninstallAppTask::IsContextReady() {