Remove barback from the repo.

pkg/barback/test/transformer/declaring_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.declaring_bad;
-
-import 'package:barback/barback.dart';
-
-import 'bad.dart';
-import 'mock.dart';
-
-/// A transformer that throws an exception when run, after generating the
-/// given outputs.
-class DeclaringBadTransformer extends MockTransformer
-    implements DeclaringTransformer {
-  /// Whether this should throw an error in [declareOutputs].
-  final bool declareError;
-
-  /// Whether this should throw an error in [apply].
-  final bool applyError;
-
-  /// The id of the output asset to emit.
-  final AssetId output;
-
-  DeclaringBadTransformer(String output, {bool declareError: true,
-          bool applyError: false})
-      : this.output = new AssetId.parse(output),
-        this.declareError = declareError,
-        this.applyError = applyError;
-
-  bool doIsPrimary(AssetId id) => true;
-
-  void doApply(Transform transform) {
-    transform.addOutput(new Asset.fromString(output, "bad out"));
-    if (applyError) throw BadTransformer.ERROR;
-  }
-
-  void declareOutputs(DeclaringTransform transform) {
-    if (consumePrimary) transform.consumePrimary();
-    transform.declareOutput(output);
-    if (declareError) throw BadTransformer.ERROR;
-  }
-}