anchor.diff:    Completer<bool> _okCancelCompleter;
   
     Future<bool> askUserOkCancel(String message,
  -      {String okButtonLabel: 'OK', String title: "", Function okAction}) {
  +      {String okButtonLabel: 'OK', String title: ""}) {
       // TODO(ussuri): Polymerize.
       if (_okCancelDialog == null) {
         _okCancelDialog = createDialog(getDialogElement('#okCancelDialog'));
  
positive.code: 
      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();
  
negative.code:   /**
     * Show a model error dialog.
     */
    void showErrorMessage(String title, String message) {
      // TODO(ussuri): Polymerize.
      if (_errorDialog == null) {
        _errorDialog = createDialog(getDialogElement('#errorDialog'));
  