Maybe some testing of, say, a few tabs, but I'd be very surprised if a significant number of Chrome devs (or any Chrome devs, for that matter) use Chromebooks for Chrome development (maybe the Chromebook Pixel, but even that seems unlikely). The Chromebook is optimized toward content consumption; while I'm sure it's possible to do serious programming on ChromeOS (just as it's possible to do serious programming on Android or (jailbroken) iOS if you really wanted to), it's not going to be nearly as productive as a high end workstation (portable or stationary) with 16+GB of RAM and a quad+ core processor.