Fix a pass-through bug in barback.

pkg/barback/lib/src/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.phase;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'asset.dart';
@@ skipping 210 matching lines @@
           _adjustTransformers(node);
         }
       }).catchError((e) {
         _adjustTransformersFutures[node.id] = new Future.error(e);
       });
     }).catchError((error) {
       if (error is! AssetNotFoundException || error.id != node.id) throw error;
 
       // If the asset is removed, [tryUntilStable] will throw an
       // [AssetNotFoundException]. In that case, just remove all transforms for
-      // the node.
+      // the node, and its pass-through.
       _transforms.remove(node.id);
+      var passThrough = _passThroughControllers.remove(node.id);
+      if (passThrough != null) passThrough.setRemoved();
     }).whenComplete(() {
       _adjustTransformersFutures.remove(node.id);
     });
 
     // Don't top-level errors coming from the input processing. Any errors will
     // eventually be piped through [process]'s returned Future.
     _adjustTransformersFutures[node.id].catchError((_) {});
   }
 
   // Remove any old transforms that used to have [asset] as a primary asset but
@@ skipping 179 matching lines @@
         // Pump the event queue to ensure that the removal of the input triggers
         // a new build to which we can attach the error.
         newFuture(() => cascade.reportError(new AssetCollisionException(
             assets.where((asset) => asset.transform != null)
                 .map((asset) => asset.transform.info),
             output.id)));
       }
     });
   }
 }