As we all — or at least SEOs and Web Developers — know by now, Google uses site speed as a factor in their ranking algorithm because in theory, a faster loading site is more useful.
This is a user agent for Google PageSpeed Insights (at least Google announces the intention in the description). Also, of note, this instance of the crawler was not part of a manual request but instead part of a quasi-regular crawl.
Http Code: 200 Date: Aug 30 09:47:41
Http Version: HTTP/1.1
Size in Bytes: 14300
Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko; Google Page Speed Insights) Chrome/27.0.1453 Safari/537.36