function extractVersion(uastring, expr, pos) {
  var match = uastring.match(expr);
  return match && match.length >= pos && parseInt(match[pos], 10);
}
Extract browser version out of the provided user agent string.

@param {!string} uastring userAgent string.
@param {!string} expr Regular expression used as match criteria.
@param {!number} pos position in the version string to be returned.
@return {!number} browser version.