Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/dart2js/allows_import_in_dart_code_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("handles imports in the Dart code", () {
-    d.dir(
-        "foo",
-        [d.libPubspec("foo", "0.0.1"), d.dir("lib", [d.file("foo.dart", """
-library foo;
-foo() => 'footext';
-""")])]).create();
-
-    d.dir(appPath, [d.appPubspec({
-        "foo": {
-          "path": "../foo"
-        }
-      }), d.dir("lib", [d.file("lib.dart", """
-library lib;
-lib() => 'libtext';
-""")]), d.dir("web", [d.file("main.dart", """
-import 'package:foo/foo.dart';
-import 'package:myapp/lib.dart';
-void main() {
-  print(foo());
-  print(lib());
-}
-""")])]).create();
-
-    pubServe(shouldGetFirst: true);
-    requestShouldSucceed("main.dart.js", contains("footext"));
-    requestShouldSucceed("main.dart.js", contains("libtext"));
-    endPubServe();
-  });
-}