function createLoafEvents(navStartEvt, {ts, duration, blockingDuration}) {
  const {pid, tid} = navStartEvt;
  ts *= 1000;
  const endTs = ts + duration * 1000;

  return [{
    name: 'LongAnimationFrame',
    ph: 'b',
    cat: 'devtools.timeline',
    pid,
    tid,
    ts,
    args: {
      data: {
        duration,
        blockingDuration,
        numScripts: 1,
        renderDuration: 14,
        styleAndLayoutDuration: 13,
      },
    },
  }, {
    name: 'LongAnimationFrame',
    ph: 'e',
    cat: 'devtools.timeline',
    pid,
    tid,
    ts: endTs,
    args: {},
  }];
}
@param {LH.TraceEvent} navStartEvt
@param {LoafDef} loafDef