Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/lish/upload_form_provides_invalid_json_test.dart

-// Copyright (c) 2013, 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();
-  setUp(d.validPackage.create);
-
-  integration('upload form provides invalid JSON', () {
-    var server = new ScheduledServer();
-    d.credentialsFile(server, 'access token').create();
-    var pub = startPublish(server);
-
-    confirmPublish(pub);
-
-    server.handle(
-        'GET',
-        '/api/packages/versions/new',
-        (request) => new shelf.Response.ok('{not json'));
-
-    pub.stderr.expect(emitsLines('Invalid server response:\n' '{not json'));
-    pub.shouldExit(1);
-  });
-}