Chrome mobile emulation user agent string

The Chrome mobile emulation user agent string is hard coded to Chrome 65.

https://github.com/WPO-Foundation/webpagetest/blob/master/www/settings/mobile_devices.ini

Was there a specific reason for this? I had expected that it would have used the same Chrome rev as the desktop version, the current release. At the time I’m writing this that was 74.

To confirm I ran a test using the real Moto G4s listed at webpagetest.org and they also use Chrome 74.