Fix a bug when loading secondary assets in barback.

pkg/barback/lib/src/graph/group_runner.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.graph.group_runner;
 
 import 'dart:async';
 
 import '../asset/asset_node.dart';
 import '../log.dart';
@@ skipping 32 matching lines @@
   /// Assets are emitted synchronously to ensure that any changes are thoroughly
   /// propagated as soon as they occur.
   Stream<AssetNode> get onAsset => _onAsset;
   Stream<AssetNode> _onAsset;
 
   /// A stream that emits an event whenever any transforms in this group logs
   /// an entry.
   Stream<LogEntry> get onLog => _onLogPool.stream;
   final _onLogPool = new StreamPool<LogEntry>.broadcast();
 
-  GroupRunner(AssetCascade cascade, this._group, this._location) {
-    _addPhase(new Phase(cascade, _location), []);
+  GroupRunner(Phase previous, this._group, this._location) {
+    _addPhase(previous.addPhase(_location), []);
     for (var phase in _group.phases) {
       _addPhase(_phases.last.addPhase(), phase);
     }
 
     _onAsset = _phases.last.onAsset;
     _onStatusChange = _phases.last.onStatusChange;
   }
 
   /// Add a phase with [contents] to [this]'s list of phases.
   ///
   /// [contents] should be an inner [Iterable] from a [TransformGroup.phases]
   /// value.
   void _addPhase(Phase phase, Iterable contents) {
     _phases.add(phase);
     _onLogPool.add(phase.onLog);
     phase.updateTransformers(contents);
   }
 
   /// Force all [LazyTransformer]s' transforms in this group to begin producing
   /// concrete assets.
   void forceAllTransforms() {
     for (var phase in _phases) {
       phase.forceAllTransforms();
     }
   }
 
-  /// Adds a new asset as an input for this group.
-  void addInput(AssetNode node) {
-    _phases.first.addInput(node);
-  }
-
   /// Removes this group and all sub-phases within it.
   void remove() {
     _onLogPool.close();
     for (var phase in _phases) {
       phase.remove();
     }
   }
 
   String toString() => "group in phase $_location for $_group";
 }