Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/lish/package_creation_provides_an_error_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 'dart:convert';
-
-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';
-import 'utils.dart';
-
-main() {
-  initConfig();
-  setUp(d.validPackage.create);
-
-  integration('package creation provides an error', () {
-    var server = new ScheduledServer();
-    d.credentialsFile(server, 'access token').create();
-    var pub = startPublish(server);
-
-    confirmPublish(pub);
-    handleUploadForm(server);
-    handleUpload(server);
-
-    server.handle('GET', '/create', (request) {
-      return new shelf.Response.notFound(JSON.encode({
-        'error': {
-          'message': 'Your package was too boring.'
-        }
-      }));
-    });
-
-    pub.stderr.expect('Your package was too boring.');
-    pub.shouldExit(1);
-  });
-}