Ensure that errors have stack traces attached.

pkg/barback/lib/src/asset_cascade.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.asset_cascade;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'asset.dart';
@@ skipping 248 matching lines @@
   Future _waitForProcess() {
     if (_processDone != null) return _processDone;
 
     _accumulatedErrors = new Queue();
     _numLogErrors = 0;
     return _processDone = _process().then((_) {
       // Report the build completion.
       // TODO(rnystrom): Put some useful data in here.
       _resultsController.add(
           new BuildResult(_accumulatedErrors));
-    }).catchError((error) {
+    }).catchError((error, stackTrace) {
       // If we get here, it's an unexpected error. Runtime errors like missing
       // assets should be handled earlier. Errors from transformers or other
       // external code that barback calls into should be caught at that API
       // boundary.
       //
       // On the off chance we get here, pipe the error to the results stream
       // as an error. That will let applications handle it without it appearing
       // in the same path as "normal" errors that get reported.
-      _resultsController.addError(error);
+      _resultsController.addError(error, stackTrace);
     }).whenComplete(() {
       _processDone = null;
       _accumulatedErrors = null;
     });
   }
 
   /// Starts the background processing.
   ///
   /// Returns a future that completes when all assets have been processed.
   Future _process() {
@@ skipping 13 matching lines @@
 
         // Otherwise, everything is done.
         return null;
       }
 
       // Process that phase and then loop onto the next.
       return future.then((_) => _process());
     });
   }
 }