Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/global/run/uses_old_lockfile_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 'package:scheduled_test/scheduled_test.dart';
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('uses the 1.6-style lockfile if necessary', () {
-    servePackages((builder) {
-      builder.serve("bar", "1.0.0");
-      builder.serve("foo", "1.0.0", deps: {
-        "bar": "any"
-      }, contents: [d.dir("bin", [d.file("script.dart", """
-              import 'package:bar/bar.dart' as bar;
-
-              main(args) => print(bar.main());""")])]);
-    });
-
-    schedulePub(args: ["cache", "add", "foo"]);
-    schedulePub(args: ["cache", "add", "bar"]);
-
-    d.dir(cachePath, [d.dir('global_packages', [d.file('foo.lock', '''
-packages:
-  foo:
-    description: foo
-    source: hosted
-    version: "1.0.0"
-  bar:
-    description: bar
-    source: hosted
-    version: "1.0.0"''')])]).create();
-
-    var pub = pubRun(global: true, args: ["foo:script"]);
-    pub.stdout.expect("bar 1.0.0");
-    pub.shouldExit();
-
-    d.dir(
-        cachePath,
-        [
-            d.dir(
-                'global_packages',
-                [
-                    d.nothing('foo.lock'),
-                    d.dir('foo', [d.matcherFile('pubspec.lock', contains('1.0.0'))])])]).validate();
-  });
-}