Fix a bug when loading secondary assets in barback.

pkg/barback/lib/src/graph/phase.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.phase;
 
 import 'dart:async';
 
 import '../asset/asset_id.dart';
 import '../asset/asset_node.dart';
@@ skipping 167 matching lines @@
       if (state.isRemoved) {
         _inputOrigins.remove(node.origin);
         _forwarders.remove(node.id).remove();
       }
       _streams.changeStatus(status);
     });
 
     for (var classifier in _classifiers.values) {
       classifier.addInput(node);
     }
-    for (var group in _groups.values) {
-      group.addInput(node);
-    }
   }
 
   // TODO(nweiz): If the output is available when this is called, it's
   // theoretically possible for it to become unavailable between the call and
   // the return. If it does so, it won't trigger the rebuilding process. To
   // avoid this, we should have this and the methods it calls take explicit
   // callbacks, as in [AssetNode.whenAvailable].
   /// Gets the asset node for an output [id].
   ///
   /// If [id] is for a generated or transformed asset, this will wait until it
@@ skipping 55 matching lines @@
     }
 
     var newGroups = transformers.where((op) => op is TransformerGroup)
         .toSet();
     var oldGroups = _groups.keys.toSet();
     for (var removed in oldGroups.difference(newGroups)) {
       _groups.remove(removed).remove();
     }
 
     for (var added in newGroups.difference(oldGroups)) {
-      var runner = new GroupRunner(cascade, added, "$_location.$_index");
+      var runner = new GroupRunner(previous, added, "$_location.$_index");
       _groups[added] = runner;
       runner.onAsset.listen(_handleOutput);
       _streams.onLogPool.add(runner.onLog);
       runner.onStatusChange.listen((_) => _streams.changeStatus(status));
-      for (var input in _inputs) {
-        runner.addInput(input);
-      }
     }
 
     for (var forwarder in _forwarders.values) {
       forwarder.updateTransformers(_classifiers.length, _groups.length);
     }
 
     _streams.changeStatus(status);
   }
 
   /// Force all [LazyTransformer]s' transforms in this phase to begin producing
   /// concrete assets.
   void forceAllTransforms() {
     for (var classifier in _classifiers.values) {
       classifier.forceAllTransforms();
     }
 
     for (var group in _groups.values) {
       group.forceAllTransforms();
     }
   }
 
   /// Add a new phase after this one.
   ///
-  /// This may only be called on a phase with no phase following it.
-  Phase addPhase() {
-    var next = new Phase._(cascade, _location, _index + 1, this);
+  /// The new phase will have a location annotation describing its place in the
+  /// package graph. By default, this annotation will describe it as being
+  /// directly after [this]. If [location] is passed, though, it's described as
+  /// being the first phase in that location.
+  Phase addPhase([String location]) {
+    var index = 0;
+    if (location == null) {
+      location = _location;
+      index = _index + 1;
+    }
+
+    var next = new Phase._(cascade, location, index, this);
     for (var output in _outputs.values.toList()) {
       // Remove [output]'s listeners because now they should get the asset from
       // [next], rather than this phase. Any transforms consuming [output] will
       // be re-run and will consume the output from the new final phase.
       output.removeListeners();
     }
     return next;
   }
 
   /// Mark this phase as removed.
@@ skipping 65 matching lines @@
     assert(asset.state.isDirty);
     asset.force();
     asset.whenStateChanges().then((state) {
       if (state.isRemoved) return getOutput(asset.id);
       return asset;
     }).then(request.complete).catchError(request.completeError);
   }
 
   String toString() => "phase $_location.$_index";
 }