constructor(bucket, path, maxZoom, opt_suffix) {
    super();

    this.bucket_ = bucket;
    this.path_ = path;
    this.suffix_ = opt_suffix || '';
    this.maxZoom_ = maxZoom;
  }
@param {string} bucket The bucket that contains the tiles.
@param {string} path The path within the bucket to the tiles.
    A trailing "/" is optional.
@param {number} maxZoom The maximum zoom level for which there are tiles.
@param {string=} opt_suffix The tile source file suffix, if any.