anchor.diff:   * in new functions that create child IFrames and run the real tests.
    */
   class ParentInteractiveHtmlConfiguration extends HtmlConfiguration {
  -  Map<int,DateTime> _testStarts;
  +  final Map<int,DateTime> _testStarts;
   
   
     /** The stack that was posted back from the child, if any. */
  
positive.code:       DateTime end = new DateTime.now();
        elapsed = end.difference(_testStarts[testCase.id]).inMilliseconds;
      }
      parentWindow.postMessage(
        _Message.text(_Message.LOG, elapsed, message).toString(), '*');
    }
  
  
negative.code:   void _handleMessage(MessageEvent e) {
      // Get the result, do any logging, then do a pass/fail.
      var msg = new _Message.fromString(e.data);
  
      if(msg == null) {
        return;
      }
      if (msg.messageType == _Message.LOG) {
        logMessage(e.data);
      } else if (msg.messageType == _Message.STACK) {
  