Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/oauth2/with_a_pre_existing_credentials_does_not_authenticate_test.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import 'package:scheduled_test/scheduled_test.dart';
-import 'package:scheduled_test/scheduled_server.dart';
-import 'package:shelf/shelf.dart' as shelf;
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('with a pre-existing credentials.json does not authenticate', () {
-    d.validPackage.create();
-
-    var server = new ScheduledServer();
-    d.credentialsFile(server, 'access token').create();
-    var pub = startPublish(server);
-    confirmPublish(pub);
-
-    server.handle('GET', '/api/packages/versions/new', (request) {
-      expect(
-          request.headers,
-          containsPair('authorization', 'Bearer access token'));
-
-      return new shelf.Response(200);
-    });
-
-    pub.kill();
-  });
-}