Add missing method - this was added to html_config but not the enhanced config.

pkg/unittest/html_enhanced_config.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 simple unit test library for running tests in a browser.
  *
  * Provides enhanced HTML output with collapsible group headers
  * and other at-a-glance information about the test results.
  */
@@ skipping 30 matching lines @@
     if (_onErrorClosure != null) {
       window.on.error.remove(_onErrorClosure);
       _onErrorClosure = null;
     }
     if (_onMessageClosure != null) {
       window.on.message.remove(_onMessageClosure);
       _onMessageClosure = null;
     }
   }
 
+  void processMessage(e) {
+    if ('unittest-suite-external-error' == e.data) {
+      handleExternalError('<unknown>', '(external error detected)');
+    }
+  }
+
   void onInit() {
     _installHandlers();
     //initialize and load CSS
     final String _CSSID = '_unittestcss_';
 
     var cssElement = document.head.query('#${_CSSID}');
     if (cssElement == null){
       document.head.elements.add(new Element.html(
           '<style id="${_CSSID}"></style>'));
       cssElement = document.head.query('#${_CSSID}');
@@ skipping 336 matching lines @@
   .unittest-row-description
   {
   }
 
   ''';
 }
 
 void useHtmlEnhancedConfiguration([bool isLayoutTest = false]) {
   configure(new HtmlEnhancedConfiguration(isLayoutTest));
 }