async destroyAllPreloads() {
    const preloadManagerDestroys = [];
    for (const preloadManager of this.createdPreloadManagers_) {
      if (!preloadManager.isDestroyed()) {
        preloadManagerDestroys.push(preloadManager.destroy());
      }
    }
    this.createdPreloadManagers_ = [];
    await Promise.all(preloadManagerDestroys);
  }
Calls |destroy| on each PreloadManager object this player has created.
@export