Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/global/activate/installs_dependencies_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 '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('activating a package installs its dependencies', () {
-    servePackages((builder) {
-      builder.serve("foo", "1.0.0", deps: {
-        "bar": "any"
-      });
-      builder.serve("bar", "1.0.0", deps: {
-        "baz": "any"
-      });
-      builder.serve("baz", "1.0.0");
-    });
-
-    schedulePub(
-        args: ["global", "activate", "foo"],
-        output: allOf(
-            [contains("Downloading bar 1.0.0..."), contains("Downloading baz 1.0.0...")]));
-  });
-}