Fix a deadlock bug with lazy transformer pipelining.

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';
@@ skipping 126 matching lines @@
             (transformer is DeclaringTransformer && primary.deferred) {
     _awaitingForce = deferred;
 
     _onLogPool.add(_onLogController.stream);
 
     _primarySubscription = primary.onStateChange.listen((state) {
       if (state.isRemoved) {
         remove();
       } else {
         if (state.isDirty && !deferred) primary.force();
+        // If this is deferred but applying, that means it must have been
+        // forced, so we should ensure its input remains forced as well.
+        if (deferred && _state == _State.APPLYING) primary.force();
         _dirty();
       }
     });
 
     _phaseSubscription = phase.previous.onAsset.listen((node) {
       if (!_missingInputs.contains(node.id)) return;
       if (!deferred) node.force();
       _dirty();
     });
 
@@ skipping 399 matching lines @@
   ///
   /// This will never transition to another state.
   static final NOT_PRIMARY = const _State._("not primary");
 
   final String name;
 
   const _State._(this.name);
 
   String toString() => name;
 }