Fix an analyzer error in barback.

pkg/barback/lib/src/phase_forwarder.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.phase_forwarder;
 
 import 'dart:async';
 
 import 'asset_node.dart';
 import 'asset_forwarder.dart';
@@ skipping 92 matching lines @@
     if (_intermediateAssets.length < _numChannels) {
       if (_outputController == null) return;
       _outputController.setRemoved();
       _outputController = null;
       return;
     }
 
     // If there isn't a final asset being forwarded yet, we should forward one.
     // It should be dirty iff any of the intermediate assets are dirty.
     if (_outputController == null) {
-      var asset = _intermediateAssets.firstWhere((asset) => asset.state.isDirty,
+      var finalAsset = _intermediateAssets.firstWhere(
+          (asset) => asset.state.isDirty,
           orElse: () => _intermediateAssets.first);
-      _outputController = new AssetNodeController.from(asset);
+      _outputController = new AssetNodeController.from(finalAsset);
       _onForwardingController.add(output);
       return;
     }
 
     // If we're already forwarding a final asset, set it dirty iff any of the
     // intermediate assets are dirty.
     if (_intermediateAssets.any((asset) => asset.state.isDirty)) {
       if (!_outputController.node.state.isDirty) _outputController.setDirty();
     } else {
       if (!_outputController.node.state.isAvailable) {
         _outputController.setAvailable(_intermediateAssets.first.asset);
       }
     }
   }
 }