static socketStartTimeIsBelowThreshold(record, mainResource) {
    const timeSinceMainEnd = Math.max(0, record.networkRequestTime - mainResource.networkEndTime);
    return timeSinceMainEnd < PRECONNECT_SOCKET_MAX_IDLE_IN_MS;
  }
Check is the connection has started before the socket idle time
@param {LH.Artifacts.NetworkRequest} record
@param {LH.Artifacts.NetworkRequest} mainResource
@return {boolean}