Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/run/errors_if_no_executable_is_given_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 '../../lib/src/exit_codes.dart' as exit_codes;
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('Errors if the executable does not exist.', () {
-    d.dir(appPath, [d.appPubspec()]).create();
-
-    schedulePub(args: ["run"], error: """
-Must specify an executable to run.
-
-Usage: pub run <executable> [args...]
--h, --help    Print this usage information.
-    --mode    Mode to run transformers in.
-              (defaults to "release" for dependencies, "debug" for entrypoint)
-
-Run "pub help" to see global options.
-""", exitCode: exit_codes.USAGE);
-  });
-}