Remove barback from the repo.

pkg/barback/test/package_graph/many_parallel_transformers_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 barback.test.package_graph.transform_test;
-
-import 'package:barback/src/utils.dart';
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../utils.dart';
-
-main() {
-  initConfig();
-
-  test("handles many parallel transformers", () {
-    currentSchedule.timeout *= 3;
-    var files = new List.generate(100, (i) => "app|$i.txt");
-    var rewrite = new RewriteTransformer("txt", "out");
-    initGraph(files, {"app": [[rewrite]]});
-
-    // Pause and resume apply to simulate parallel long-running transformers.
-    rewrite.pauseApply();
-    updateSources(files);
-    schedule(pumpEventQueue);
-    rewrite.resumeApply();
-
-    for (var i = 0; i < 100; i++) {
-      expectAsset("app|$i.out", "$i.out");
-    }
-    buildShouldSucceed();
-  });
-}