static _isNavigationStartOfInterest(event) {
    if (event.name !== 'navigationStart') return false;
    // COMPAT: support pre-m67 test traces before `args.data` added to all navStart events.
    // TODO: remove next line when old test traces (e.g. progressive-app-m60.json) are updated.
    if (event.args.data?.documentLoaderURL === undefined) return true;
    if (!event.args.data?.documentLoaderURL) return false;
    return ACCEPTABLE_NAVIGATION_URL_REGEX.test(event.args.data.documentLoaderURL);
  }
Returns true if the event is a navigation start event of a document whose URL seems valid.

@param {LH.TraceEvent} event
@return {boolean}