formatTileUrl = (x, y, z) => {
    const width = Math.pow(2, z);
    x = x % width;
    x = String(x < 0 ? x + width : x);  // JSCompiler: replace() needs string.
    return urlFormat.replace('{x}', x).replace('{y}', y).replace('{z}', z);
  }
Constructs a RawMapId, generating formatTileUrl and urlFormat from mapid and
token.
@param {string} mapid Map ID.
@param {string} token Token.  Will only be non-empty when using legacy API.
@param {string=} opt_urlFormat Explicit URL format.  Overrides the format
   inferred from mapid and token.
@return {!ee.data.RawMapId}
@private