Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/transformer/a_transformer_rejects_its_config_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.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.
-
-library pub_tests;
-
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import '../serve/utils.dart';
-
-const REJECT_CONFIG_TRANSFORMER = """
-import 'dart:async';
-
-import 'package:barback/barback.dart';
-
-class RejectConfigTransformer extends Transformer {
-  RejectConfigTransformer.asPlugin(BarbackSettings settings) {
-    throw "I hate these settings!";
-  }
-
-  Future<bool> isPrimary(_) => new Future.value(true);
-  Future apply(Transform transform) {}
-}
-""";
-
-main() {
-  initConfig();
-
-  withBarbackVersions("any", () {
-    integration("a transformer can reject is configuration", () {
-      d.dir(appPath, [d.pubspec({
-          "name": "myapp",
-          "transformers": [{
-              "myapp/src/transformer": {
-                'foo': 'bar'
-              }
-            }]
-        }),
-            d.dir(
-                "lib",
-                [
-                    d.dir(
-                        "src",
-                        [d.file("transformer.dart", REJECT_CONFIG_TRANSFORMER)])])]).create();
-
-      createLockFile('myapp', pkg: ['barback']);
-
-      var pub = startPubServe();
-      pub.stderr.expect(
-          endsWith('Error loading transformer: I hate these ' 'settings!'));
-      pub.shouldExit(1);
-    });
-  });
-}