Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/global/activate/outdated_binstub_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 'dart:io';
-import 'dart:async';
-
-import 'package:path/path.dart' as p;
-import 'package:scheduled_test/scheduled_process.dart';
-import 'package:scheduled_test/scheduled_stream.dart';
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-const _OUTDATED_BINSTUB = """
-#!/usr/bin/env sh
-# This file was created by pub v0.1.2-3.
-# Package: foo
-# Version: 1.0.0
-# Executable: foo-script
-# Script: script
-dart "/path/to/.pub-cache/global_packages/foo/bin/script.dart.snapshot" "\$@"
-""";
-
-main() {
-  initConfig();
-  integration("an outdated binstub is replaced", () {
-    servePackages((builder) {
-      builder.serve("foo", "1.0.0", pubspec: {
-        "executables": {
-          "foo-script": "script"
-        }
-      },
-          contents: [
-              d.dir("bin", [d.file("script.dart", "main(args) => print('ok \$args');")])]);
-    });
-
-    schedulePub(args: ["global", "activate", "foo"]);
-
-    d.dir(
-        cachePath,
-        [
-            d.dir('bin', [d.file(binStubName('foo-script'), _OUTDATED_BINSTUB)])]).create();
-
-    schedulePub(args: ["global", "activate", "foo"]);
-
-    d.dir(
-        cachePath,
-        [d.dir('bin', [// 255 is the VM's exit code upon seeing an out-of-date snapshot.
-        d.matcherFile(
-            binStubName('foo-script'),
-            contains("255"))])]).validate();
-  });
-}