Remove barback from the repo.

pkg/barback/test/transformer/lazy_bad.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.transformer.lazy_bad;
-
-import 'package:barback/barback.dart';
-
-import 'mock.dart';
-
-/// A lazy transformer that throws an exception after [declareOutputs].
-class LazyBadTransformer extends MockTransformer implements LazyTransformer {
-  /// The error [this] throws.
-  static const ERROR = "I am a bad transformer!";
-
-  /// The asset name that [this] should output.
-  final String output;
-
-  LazyBadTransformer(this.output);
-
-  bool doIsPrimary(AssetId id) => true;
-
-  void doApply(Transform transform) {
-    var id = new AssetId.parse(output);
-    transform.addOutput(new Asset.fromString(id, output));
-  }
-
-  void declareOutputs(DeclaringTransform transform) {
-    var id = new AssetId.parse(output);
-    transform.declareOutput(id);
-    throw ERROR;
-  }
-}