Only pass an AssetId to isPrimary and declareOutputs.

pkg/barback/lib/src/transform_node.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.transform_node;
 
 import 'dart:async';
 
 import 'asset.dart';
 import 'asset_id.dart';
@@ skipping 173 matching lines @@
 
   /// Determines whether [primary] is primary for [transformer], and if so runs
   /// [transformer.apply].
   void _process() {
     // Clear all the old input subscriptions. If an input is re-used, we'll
     // re-subscribe.
     _clearInputSubscriptions();
     _state = _TransformNodeState.PROCESSING;
     primary.whenAvailable((_) {
       _state = _TransformNodeState.PROCESSING;
-      return transformer.isPrimary(primary.asset);
+      return transformer.isPrimary(primary.asset.id);
     }).catchError((error, stackTrace) {
       // If the transform became dirty while processing, ignore any errors from
       // it.
       if (_state.needsIsPrimary || _isRemoved) return false;
 
       // Catch all transformer errors and pipe them to the results stream. This
       // is so a broken transformer doesn't take down the whole graph.
       phase.cascade.reportError(_wrapException(error, stackTrace));
 
       return false;
@@ skipping 301 matching lines @@
   ///
   /// Specifically, whether [this] is [APPLIED] or [NOT_PRIMARY].
   bool get isDone => isApplied || isNotPrimary;
 
   final String name;
 
   const _TransformNodeState._(this.name);
 
   String toString() => name;
 }