Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/serve/web_socket/url_to_asset_id_errors_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 '../utils.dart';
-
-main() {
-  initConfig();
-  setUp(() {
-    d.dir(appPath, [d.appPubspec()]).create();
-  });
-
-  integration("responds with NOT_SERVED for an unknown domain", () {
-    pubServe();
-    expectWebSocketError("urlToAssetId", {
-      "url": "http://example.com:80/index.html"
-    }, NOT_SERVED, '"example.com:80" is not being served by pub.');
-    endPubServe();
-  });
-
-  integration("responds with NOT_SERVED for an unknown port", () {
-    pubServe();
-    expectWebSocketError("urlToAssetId", {
-      "url": "http://localhost:80/index.html"
-    }, NOT_SERVED, '"localhost:80" is not being served by pub.');
-    endPubServe();
-  });
-}