Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/run/passes_along_arguments_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS 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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-const SCRIPT = """
-main(List<String> args) {
-  print(args.join(" "));
-}
-""";
-
-main() {
-  initConfig();
-  integration('passes arguments to the spawned script', () {
-    d.dir(
-        appPath,
-        [d.appPubspec(), d.dir("bin", [d.file("args.dart", SCRIPT)])]).create();
-
-    // Use some args that would trip up pub's arg parser to ensure that it
-    // isn't trying to look at them.
-    var pub = pubRun(args: ["args", "--verbose", "-m", "--", "help"]);
-
-    pub.stdout.expect("--verbose -m -- help");
-    pub.shouldExit();
-  });
-}