The first beta version of the Google Chrome browser has an user agent string of its own, and although it will change with the next version, it will most likely follow the same format thus making it safe to implement into your current code:

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/0.2.149.27 Safari/525.13