Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/transformer/configuration/configuration_defaults_to_empty_map_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 file.
-
-library pub_tests;
-
-import 'dart:convert';
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-import '../../serve/utils.dart';
-
-final transformer = """
-import 'dart:async';
-import 'dart:convert';
-
-import 'package:barback/barback.dart';
-
-class ConfigTransformer extends Transformer {
-  final BarbackSettings settings;
-
-  ConfigTransformer.asPlugin(this.settings);
-
-  String get allowedExtensions => '.txt';
-
-  Future apply(Transform transform) {
-    return transform.primaryInput.readAsString().then((contents) {
-      var id = transform.primaryInput.id.changeExtension(".json");
-      transform.addOutput(
-          new Asset.fromString(id, JSON.encode(settings.configuration)));
-    });
-  }
-}
-""";
-
-main() {
-  initConfig();
-  withBarbackVersions("any", () {
-    integration("configuration defaults to an empty map", () {
-      d.dir(appPath, [d.pubspec({
-          "name": "myapp",
-          "transformers": ["myapp/src/transformer"]
-        }),
-            d.dir("lib", [d.dir("src", [d.file("transformer.dart", transformer)])]),
-            d.dir("web", [d.file("foo.txt", "foo")])]).create();
-
-      createLockFile('myapp', pkg: ['barback']);
-
-      var server = pubServe();
-      requestShouldSucceed("foo.json", JSON.encode({}));
-      endPubServe();
-    });
-  });
-}