Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/test/transformer/loads_an_aggregate_transformer_test.dart

-// Copyright (c) 2014, 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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-import '../serve/utils.dart';
-
-const AGGREGATE_TRANSFORMER = """
-import 'dart:async';
-
-import 'package:barback/barback.dart';
-import 'package:path/path.dart' as p;
-
-class ManyToOneTransformer extends AggregateTransformer {
-  ManyToOneTransformer.asPlugin();
-
-  String classifyPrimary(AssetId id) {
-    if (id.extension != '.txt') return null;
-    return p.url.dirname(id.path);
-  }
-
-  Future apply(AggregateTransform transform) {
-    return transform.primaryInputs.toList().then((assets) {
-      assets.sort((asset1, asset2) => asset1.id.path.compareTo(asset2.id.path));
-      return Future.wait(assets.map((asset) => asset.readAsString()));
-    }).then((contents) {
-      var id = new AssetId(transform.package,
-          p.url.join(transform.key, 'out.txt'));
-      transform.addOutput(new Asset.fromString(id, contents.join('\\n')));
-    });
-  }
-}
-""";
-
-main() {
-  initConfig();
-  withBarbackVersions(">=0.14.1", () {
-    integration("loads an aggregate transformer", () {
-      d.dir(appPath, [d.pubspec({
-          "name": "myapp",
-          "transformers": ["myapp"]
-        }),
-            d.dir("lib", [d.file("transformer.dart", AGGREGATE_TRANSFORMER),]),
-            d.dir("web", [d.file("foo.txt", "foo"), d.file("bar.txt", "bar")])]).create();
-
-      createLockFile('myapp', pkg: ['barback']);
-
-      pubServe();
-      requestShouldSucceed("out.txt", "bar\nfoo");
-      endPubServe();
-    });
-  });
-}