createDialog(dialogDomHelper) {
    const dialog = new goog.demos.editor.HelloWorldDialog(dialogDomHelper);
    dialog.addEventListener(
        goog.ui.editor.AbstractDialog.EventType.OK, this.handleOk_, false,
        this);
    return dialog;
  }
Creates a new instance of the dialog and registers for the relevant events.
@param {goog.dom.DomHelper} dialogDomHelper The dom helper to be used to
    create the dialog.
@return {!goog.demos.editor.HelloWorldDialog} The dialog.
@override
@protected