Only pass an AssetId to isPrimary and declareOutputs.

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 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:barback/src/utils.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);
 
-  Future<bool> doIsPrimary(Asset asset) => new Future.value(true);
+  Future<bool> doIsPrimary(AssetId id) => new Future.value(true);
 
   Future doApply(Transform transform) {
     return newFuture(() {
       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));
       }
     });
   }
 }