constructor(getFilterRange) {
    super();

    /** @private {!Map<string, T>} */
    this.regions_ = new Map();

    /** @private {!function():{start: number, end: number}} */
    this.getFilterRange_ = getFilterRange;

    /**
     * Make sure all of the regions we're tracking are within the
     * seek range or further in the future. We don't want to store
     * regions that fall before the start of the seek range.
     *
     * @private {shaka.util.Timer}
     */
    this.filterTimer_ = null;
  }
@param {!function():{start: number, end: number}} getFilterRange