setUpdateTimer_() {
    if (this.updatePeriod_ <= 0) {
      return;
    }

    const finalDelay = Math.max(
        shaka.mss.MssParser.MIN_UPDATE_PERIOD_,
        this.updatePeriod_,
        this.averageUpdateDuration_.getEstimate());

    // We do not run the timer as repeating because part of update is async and
    // we need schedule the update after it finished.
    this.updateTimer_.tickAfter(/* seconds= */ finalDelay);
  }
Sets the update timer.  Does nothing if the manifest is not live.

@private