getTileUrl_(coord, zoom) {
    var url = stringPath.join(
        CloudStorageTileSource.BASE_URL, this.bucket_, this.path_, String(zoom),
        String(coord.x), String(coord.y));
    if (this.suffix_) {
      url += this.suffix_;
    }
    return url;
  }
Generates the Cloud Storage URL for the tile at the given location and
zoom.
@param {!google.maps.Point} coord The position of the tile.
@param {number} zoom The zoom level of the tile.
@return {string} The tile URL.
@private