Re-run a transform when a secondary input starts existing.

pkg/barback/lib/src/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.group_runner;
 
 import 'dart:async';
 
 import 'asset_cascade.dart';
 import 'asset_node.dart';
@@ skipping 35 matching lines @@
   /// 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), _group.phases.first);
-    for (var phase in _group.phases.skip(1)) {
+    _addPhase(new Phase(cascade, _location), []);
+    for (var phase in _group.phases) {
       _addPhase(_phases.last.addPhase(), phase);
     }
 
     _onAsset = _phases.last.onAsset;
     _onDone = _phases.last.onDone;
   }
 
   /// Add a phase with [contents] to [this]'s list of phases.
   ///
   /// [contents] should be an inner [Iterable] from a [TransformGroup.phases]
@@ skipping 19 matching lines @@
 
   /// Removes this group and all sub-phases within it.
   void remove() {
     for (var phase in _phases) {
       phase.remove();
     }
   }
 
   String toString() => "group in phase $_location for $_group";
 }