Latest Headless Chrome 59 user agents:

User Agent Platform Device
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/59.0.3071.115 Safari/537.36 GNU/Linux Unknown
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/59.0.3071.109 Safari/537.36 GNU/Linux Unknown