function saveTrace(traceData, traceFilename, options = {}) {
  const traceIter = traceJsonGenerator(traceData);
  return writeJson(traceIter, traceFilename, !!options.gzip);
}
Save a trace as JSON by streaming to disk at traceFilename.
@param {LH.Trace} traceData
@param {string} traceFilename
@param {{gzip?: boolean}=} options
@return {Promise<void>}