Fix cancelable_future again.

pkg/barback/test/transformer/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.bad;
+
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:barback/src/utils.dart';
 
 import 'mock.dart';
 
 /// A transformer that throws an exception when run, after generating the
 /// given outputs.
 class BadTransformer extends MockTransformer {
@@ skipping 13 matching lines @@
       for (var output in outputs) {
         var id = new AssetId.parse(output);
         transform.addOutput(new Asset.fromString(id, output));
       }
 
       // Then fail.
       throw ERROR;
     });
   }
 }