pkg/barback: removed unused imports, added a missing import

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';
 import 'asset_node.dart';
 import 'asset_set.dart';
 import 'errors.dart';
 import 'phase.dart';
 import 'transform.dart';
 import 'transformer.dart';
-import 'utils.dart';
 
 /// Describes a transform on a set of assets and its relationship to the build
 /// dependency graph.
 ///
 /// Keeps track of whether it's dirty and needs to be run and which assets it
 /// depends on.
 class TransformNode {
   /// The [Phase] that this transform runs in.
   final Phase phase;
 
@@ skipping 167 matching lines @@
       } else {
         var controller = new AssetNodeController.available(asset, this);
         _outputControllers[asset.id] = controller;
         brandNewOutputs.add(controller.node);
       }
     }
 
     return brandNewOutputs;
   }
 }