Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/dart2js/source_maps_include_core_libs_in_subdirectory_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:path/path.dart' as path;
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../descriptor.dart' as d;
-import '../serve/utils.dart';
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-
-  // This test is a bit shaky. Since dart2js is free to inline things, it's
-  // not precise as to which source libraries will actually be referenced in
-  // the source map. But this tries to use a type in the core library
-  // (StringBuffer) and validate that its source ends up in the source map.
-  integration(
-      "Dart core libraries are available to source maps when the "
-          "build directory is a subdirectory",
-      () {
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir(
-                "web",
-                [
-                    d.dir(
-                        "sub",
-                        [
-                            d.file(
-                                "main.dart",
-                                "main() => new StringBuffer().writeAll(['s']);")])])]).create();
-
-    var webSub = path.join("web", "sub");
-    pubServe(args: [webSub]);
-
-    requestShouldSucceed(
-        "main.dart.js.map",
-        contains(r"packages/$sdk/lib/core/string_buffer.dart"),
-        root: webSub);
-    requestShouldSucceed(
-        r"packages/$sdk/lib/core/string_buffer.dart",
-        contains("class StringBuffer"),
-        root: webSub);
-
-    endPubServe();
-  });
-}