Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/lish/upload_form_url_is_not_a_string_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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-main() {
-  initConfig();
-  setUp(d.validPackage.create);
-
-  integration('upload form url is not a string', () {
-    var server = new ScheduledServer();
-    d.credentialsFile(server, 'access token').create();
-    var pub = startPublish(server);
-
-    confirmPublish(pub);
-
-    var body = {
-      'url': 12,
-      'fields': {
-        'field1': 'value1',
-        'field2': 'value2'
-      }
-    };
-
-    handleUploadForm(server, body);
-    pub.stderr.expect('Invalid server response:');
-    pub.stderr.expect(JSON.encode(body));
-    pub.shouldExit(1);
-  });
-}