[SyncFS] Construct and destruct sync_worker in worker_task_runner

chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc

Index: chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc b/chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc
index b528b52d5c6d3431672953270aec4d7f0b1647a3..d61c8afbe1274b49cc9b6504a4030a0a3014036d 100644
--- a/chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc
+++ b/chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc
@@ -82,11 +82,15 @@ class DriveBackendSyncTest : public testing::Test,
         file_task_runner_.get(),
         NULL, NULL, NULL));
     remote_sync_service_->AddServiceObserver(this);
+
+    base::RunLoop run_loop;
     remote_sync_service_->Initialize(base_dir_.path(),
                                      base::MessageLoopProxy::current(),
+                                     run_loop.QuitClosure(),
                                      in_memory_env_.get());
-    remote_sync_service_->SetSyncEnabled(true);
+    run_loop.Run();
 
+    remote_sync_service_->SetSyncEnabled(true);
     local_sync_service_->SetLocalChangeProcessor(remote_sync_service_.get());
     remote_sync_service_->SetRemoteChangeProcessor(local_sync_service_.get());
   }