Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/upgrade/report/highlights_overrides_test.dart

-// Copyright (c) 2013, 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.
-
-library pub_tests;
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration("highlights overridden packages", () {
-    servePackages((builder) => builder.serve("overridden", "1.0.0"));
-
-    d.dir(appPath, [d.pubspec({
-        "name": "myapp",
-        "dependency_overrides": {
-          "overridden": "any"
-        }
-      })]).create();
-
-    // Upgrade everything.
-    pubUpgrade(output: new RegExp(r"""
-Resolving dependencies\.\.\..*
-! overridden 1\.0\.0 \(overridden\)
-""", multiLine: true));
-  });
-}