Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/dart2js/does_not_support_invalid_option_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.
-
-import '../../lib/src/exit_codes.dart' as exit_codes;
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import '../serve/utils.dart';
-
-main() {
-  initConfig();
-  integration("doesn't support an invalid dart2js option", () {
-    d.dir(appPath, [d.pubspec({
-        "name": "myapp",
-        "transformers": [{
-            "\$dart2js": {
-              "invalidOption": true
-            }
-          }]
-      })]).create();
-
-    // TODO(nweiz): This should provide more context about how the option got
-    // passed to dart2js. See issue 16008.
-    var pub = startPubServe();
-    pub.stderr.expect('Unrecognized dart2js option "invalidOption".');
-    pub.shouldExit(exit_codes.DATA);
-  });
-}