Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/get/hosted/cached_pubspec_test.dart

-// Copyright (c) 2012, 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 'package:scheduled_test/scheduled_test.dart';
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-
-  integration('does not request a pubspec for a cached package', () {
-    servePackages((builder) => builder.serve("foo", "1.2.3"));
-
-    d.appDir({
-      "foo": "1.2.3"
-    }).create();
-
-    // Get once so it gets cached.
-    pubGet();
-
-    // Clear the cache. We don't care about anything that was served during
-    // the initial get.
-    getRequestedPaths();
-
-    d.cacheDir({
-      "foo": "1.2.3"
-    }).validate();
-    d.packagesDir({
-      "foo": "1.2.3"
-    }).validate();
-
-    // Run the solver again now that it's cached.
-    pubGet();
-
-    // The get should not have requested the pubspec since it's local already.
-    getRequestedPaths().then((paths) {
-      expect(paths, isNot(contains("packages/foo/versions/1.2.3.yaml")));
-    });
-  });
-}