fix build after clang roll

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 a43465f95aebfa060911538f68ee013fe7d01413..f87a65a527f45964bef4aa9c686508654c4493d4 100644
--- a/chrome/browser/sync_file_system/drive_backend/sync_engine.h
+++ b/chrome/browser/sync_file_system/drive_backend/sync_engine.h
@@ -140,8 +140,9 @@ class SyncEngine : public RemoteFileSyncService,
   ObserverList<FileStatusObserver> file_status_observers_;
   RemoteChangeProcessor* remote_change_processor_;
 
-  SyncTaskManager task_manager_;
+  // TODO: This should be the last member in this class.
   base::WeakPtrFactory<SyncEngine> weak_ptr_factory_;
+  SyncTaskManager task_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncEngine);
 };