static dispatchLoadedEvent_(eventName, reasonCode) {
    let detail = null;
    if (reasonCode != undefined) {
      detail = {
        'reasonCode': reasonCode,
      };
    }
    const uiLoadedEvent = new CustomEvent(eventName, {detail});
    document.dispatchEvent(uiLoadedEvent);
  }
@param {string} eventName
@param {shaka.ui.Overlay.FailReasonCode=} reasonCode
@private