Only pass an AssetId to isPrimary and declareOutputs.

pkg/barback/test/transformer/one_to_many.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.one_to_many;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 import 'mock.dart';
 
 /// A [Transformer] that takes an input asset that contains a comma-separated
 /// list of paths and outputs a file for each path.
 class OneToManyTransformer extends MockTransformer {
   final String extension;
 
   /// Creates a transformer that consumes assets with [extension].
   ///
   /// That file contains a comma-separated list of paths and it will output
   /// files at each of those paths.
   OneToManyTransformer(this.extension);
 
-  Future<bool> doIsPrimary(Asset asset) =>
-    new Future.value(asset.id.extension == ".$extension");
+  Future<bool> doIsPrimary(AssetId id) =>
+    new Future.value(id.extension == ".$extension");
 
   Future doApply(Transform transform) {
     return getPrimary(transform)
         .then((input) => input.readAsString())
         .then((lines) {
       for (var line in lines.split(",")) {
         var id = new AssetId(transform.primaryInput.id.package, line);
         transform.addOutput(new Asset.fromString(id, "spread $extension"));
       }
     });
   }
 
   String toString() => "1->many $extension";
 }