Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/transformer/exclusion/works_on_dart2js_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_stream.dart';
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-import '../../serve/utils.dart';
-
-main() {
-  initConfig();
-  withBarbackVersions("any", () {
-    integration("works on the dart2js transformer", () {
-      d.dir(appPath, [d.pubspec({
-          "name": "myapp",
-          "transformers": [{
-              "\$dart2js": {
-                "\$include": ["web/a.dart", "web/b.dart"],
-                "\$exclude": "web/a.dart"
-              }
-            }]
-        }),
-            d.dir(
-                "web",
-                [
-                    d.file("a.dart", "void main() => print('hello');"),
-                    d.file("b.dart", "void main() => print('hello');"),
-                    d.file("c.dart", "void main() => print('hello');")])]).create();
-
-      createLockFile('myapp', pkg: ['barback']);
-
-      var server = pubServe();
-      // Dart2js should remain lazy.
-      server.stdout.expect("Build completed successfully");
-
-      requestShould404("a.dart.js");
-      requestShouldSucceed("b.dart.js", isNot(isEmpty));
-      server.stdout.expect(
-          consumeThrough(
-              emitsLines("[Info from Dart2JS]:\n" "Compiling myapp|web/b.dart...")));
-      server.stdout.expect(consumeThrough("Build completed successfully"));
-
-      requestShould404("c.dart.js");
-      endPubServe();
-    });
-  });
-}