Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/get/path/empty_pubspec_test.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 d.file.
-
-import 'package:path/path.dart' as p;
-
-import '../../../lib/src/exit_codes.dart' as exit_codes;
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  // Regression test for issue 20103.
-  integration('path dependency to an empty pubspec', () {
-    d.dir('foo', [d.libDir('foo'), d.file('pubspec.yaml', '')]).create();
-
-    d.dir(appPath, [d.appPubspec({
-        "foo": {
-          "path": "../foo"
-        }
-      })]).create();
-
-    pubGet(
-        exitCode: exit_codes.DATA,
-        error: 'Error on line 1, column 1 of ${p.join('..', 'foo', 'pubspec.yaml')}: '
-            'Missing the required "name" field.');
-  });
-}