Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/test/dart2js/converts_isolate_entrypoint_in_web_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 'package:scheduled_test/scheduled_test.dart';
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import '../serve/utils.dart';
-
-main() {
-  initConfig();
-  integration("converts a Dart isolate entrypoint in web to JS", () {
-    // Increase the timeout because dart2js takes a lot longer than usual to
-    // compile isolate entrypoints.
-    currentSchedule.timeout *= 2;
-
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir(
-                "web",
-                [
-                    d.file(
-                        "isolate.dart",
-                        "void main(List<String> args, SendPort "
-                            "sendPort) => print('hello');")])]).create();
-
-    pubServe();
-    requestShouldSucceed("isolate.dart.js", contains("hello"));
-    endPubServe();
-  });
-}