Update [getErrorMessage] to avoid throwing away useful information.

pkg/barback/lib/src/serialize.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.serialize;
 
 import 'dart:async';
 import 'dart:isolate';
 
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 96 matching lines @@
     return {
       'type': error.runtimeType.toString(),
       'message': _getErrorMessage(error),
       'stack': stack == null ? null : new Chain.forTrace(stack).toString()
     };
   }
 
   String toString() => "$message\n$stackTrace";
 }
 
-// Get a string description of an exception.
-//
-// Most exception types have a "message" property. We prefer this since
-// it skips the "Exception:", "HttpException:", etc. prefix that calling
-// toString() adds. But, alas, "message" isn't actually defined in the
-// base Exception type so there's no easy way to know if it's available
-// short of a giant pile of type tests for each known exception type.
-//
-// So just try it. If it throws, default to toString().
-String _getErrorMessage(error) {
-  try {
-    return error.message;
-  } on NoSuchMethodError catch (_) {
-    return error.toString();
-  }
-}
+/// A regular expression to match the exception prefix that some exceptions'
+/// [Object.toString] values contain.
+final _exceptionPrefix = new RegExp(r'^([A-Z][a-zA-Z]*)?(Exception|Error): ');
+
+/// Get a string description of an exception.
+///
+/// Many exceptions include the exception class name at the beginning of their
+/// [toString], so we remove that if it exists.
+String _getErrorMessage(error) =>
+  error.toString().replaceFirst(_exceptionPrefix, '');