Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/serve/serves_web_and_test_dirs_by_default_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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-main() {
-  initConfig();
-  integration("serves web/ and test/ dirs by default", () {
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir("web", [d.file("foo", "contents")]),
-            d.dir("test", [d.file("bar", "contents")]),
-            d.dir("example", [d.file("baz", "contents")])]).create();
-
-    pubServe();
-    requestShouldSucceed("foo", "contents", root: "web");
-    requestShouldSucceed("bar", "contents", root: "test");
-    requestShould404("baz", root: "web");
-    endPubServe();
-  });
-}