anchor.diff:      }
   
       if (props_exist) {
  -      print('Found JavaScript property ${prop_string}');
  +      _log.finest('Found JavaScript property ${prop_string}');
         completer.complete(obj);
       } else {
         new Timer(PROPERTY_POLL_INTERVAL, completeIfJsAttrExists);
  
positive.code:       onLoad(JSON.decode(httpRequest.responseText));
      } else {
        if (onError == null) {
          print('HttpRequest error: ${e.toString()}');
        } else {
          onError(httpRequest, e);
        }
  
negative.code: //
  // The future returns the JsObject corresponding to the property.
  Future<JsObject> whenJsPropExists(String prop_string) {
    final Logger _log = new Logger('whenJsPropExists');
    const Duration PROPERTY_POLL_INTERVAL = const Duration(milliseconds: 25);
    final List<String> props = prop_string.split('.');
  
  