anchor.diff:  
       SparkDialogButton okButton = _okCancelDialog.getElement('#okText');
       _okCancelDialog.getElement('#okText').text = okButtonLabel;
  -
  -    if (okAction != null) {
  -      okButton.onClick.listen((_) {
  -        // Ensures that errorDialog closes before the action.
  -        Timer.run(() {
  -          okAction();
  -        });
  -      });
  -    }
   
       _okCancelCompleter = new Completer();
       _okCancelDialog.show();
  
positive.code:   /**
     * Show a model error dialog.
     */
    void showErrorMessage(
        String title, String message) {
      // TODO(ussuri): Polymerize.
      if (_errorDialog == null) {
        _errorDialog = createDialog(getDialogElement('#errorDialog'));
  
negative.code:   Completer<bool> _okCancelCompleter;
  
    Future<bool> askUserOkCancel(String message,
        {String okButtonLabel: 'OK', String title: ""}) {
      // TODO(ussuri): Polymerize.
      if (_okCancelDialog == null) {
        _okCancelDialog = createDialog(getDialogElement('#okCancelDialog'));
  