Pipe the stack traces of errors through Future operations.

corelib/src/future.dart

 // Copyright (c) 2011, 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.
 
 /**
  * A [Future] is used to obtain a value sometime in the future.  Receivers of a
  * [Future] can obtain the value by passing a callback to [then]. For example:
  *
  *     Future<int> future = getFutureFromSomewhere();
  *     future.then((value) {
@@ skipping 199 matching lines @@
       // http://code.google.com/p/dart/issues/detail?id=333 is fixed.
       int pos = i;
       Future future = futures[pos];
       future.then((Object value) {
         values[pos] = value;
         if (--remaining == 0 && !result.isComplete) {
           completer.complete(values);
         }
       });
       future.handleException((exception) {
-        if (!result.isComplete) completer.completeException(exception);
+        if (!result.isComplete) {
+          completer.completeException(exception, future.stackTrace);
+        }
         return true;
       });
     }
     return result;
   }
 }