Use native async/await support in pub.

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

-// Copyright (c) 2013, 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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-import '../serve/utils.dart';
-
-main() {
-  initConfig();
-  withBarbackVersions("any", () {
-    integration("runs a third-party transformer on a local transformer", () {
-      d.dir(
-          "foo",
-          [
-              d.libPubspec("foo", '1.0.0'),
-              d.dir("lib", [d.file("transformer.dart", dartTransformer('foo'))])]).create();
-
-      d.dir(appPath, [d.pubspec({
-          "name": "myapp",
-          "transformers": ["foo/transformer", "myapp/transformer"],
-          "dependencies": {
-            "foo": {
-              "path": "../foo"
-            }
-          }
-        }),
-            d.dir("lib", [d.file("transformer.dart", dartTransformer('myapp'))]),
-            d.dir("web", [d.file("main.dart", 'const TOKEN = "main.dart";')])]).create();
-
-      createLockFile('myapp', sandbox: ['foo'], pkg: ['barback']);
-
-      pubServe();
-      requestShouldSucceed(
-          "main.dart",
-          'const TOKEN = "((main.dart, foo), (myapp, foo))";');
-      endPubServe();
-    });
-  });
-}