activateChaptersTrack_(track) {
    if (!track || track.kind != 'chapters') {
      return;
    }

    // Hidden mode is required for the cuechange event to launch correctly and
    // get the cues and the activeCues
    track.mode = 'hidden';

    // In Safari the initial assignment does not always work, so we schedule
    // this process to be repeated several times to ensure that it has been put
    // in the correct mode.
    const timer = new shaka.util.Timer(() => {
      track.mode = 'hidden';
    }).tickNow().tickAfter(0.5);

    this.cleanupOnUnload_.push(() => {
      timer.stop();
    });
  }
Set the mode on a chapters track so that it loads.

@param {?TextTrack} track
@private