Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/dart2js/compiles_generated_file_from_dependency_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();
-  withBarbackVersions("any", () {
-    integration(
-        "compiles a Dart file that imports a generated file in another "
-            "package to JS",
-        () {
-      d.dir("foo", [d.pubspec({
-          "name": "foo",
-          "version": "0.0.1",
-          "transformers": ["foo/transformer"]
-        }), d.dir("lib", [d.file("foo.dart", """
-library foo;
-const TOKEN = "before";
-foo() => TOKEN;
-"""), d.file("transformer.dart", dartTransformer("munge"))])]).create();
-
-      d.dir(appPath, [d.appPubspec({
-          "foo": {
-            "path": "../foo"
-          }
-        }), d.dir("web", [d.file("main.dart", """
-import "package:foo/foo.dart";
-main() => print(foo());
-""")])]).create();
-
-      createLockFile("myapp", sandbox: ["foo"], pkg: ["barback"]);
-
-      pubServe();
-      requestShouldSucceed("main.dart.js", contains("(before, munge)"));
-      endPubServe();
-    });
-  });
-}