Remove barback from the repo.

pkg/barback/test/transformer/bad_log.dart

-// Copyright (c) 2014, 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.transformer.bad_log;
-
-import 'package:barback/barback.dart';
-
-import 'mock.dart';
-
-/// A transformer that logs an error when run, Before generating the given
-/// outputs.
-class BadLogTransformer extends MockTransformer {
-  /// The list of asset names that it should output.
-  final List<String> outputs;
-
-  BadLogTransformer(this.outputs);
-
-  bool doIsPrimary(AssetId id) => true;
-
-  void doApply(Transform transform) {
-    transform.logger.error("first error");
-    transform.logger.error("second error");
-
-    for (var output in outputs) {
-      var id = new AssetId.parse(output);
-      transform.addOutput(new Asset.fromString(id, output));
-    }
-  }
-}