anchor.diff:      void onLoad(Map responseJson),
       {void onError(HttpRequest request, ProgressEvent e),
        String method: 'POST'}) {
  +  final Logger _log = new Logger('postJson');
     HttpRequest httpRequest = new HttpRequest();
     httpRequest.open(method, url);
     httpRequest.setRequestHeader(
  
positive.code:     }
  
      if (props_exist) {
        print('Found JavaScript property ${prop_string}');
        completer.complete(obj);
      } else {
        new Timer(PROPERTY_POLL_INTERVAL, completeIfJsAttrExists);
  
negative.code:       onLoad(JSON.decode(httpRequest.responseText));
      } else {
        if (onError == null) {
          _log.warning('HttpRequest error: ${e.toString()}');
        } else {
          onError(httpRequest, e);
        }
  