I haven't worked at Google in a few years. At the time I was there, most engineers were still using Windows or Linux. Chrome OS was in its infancy. I'd estimate only around two hundred engineers used Chrome OS and gave us feedback about it, prior to my leaving Google in 2008.
Macs have become more popular recently since Mac OS is a Unix, and Google is first and foremost of Linux company.
(More) Does every Googler own a MacBook?
via Answers by Jeff Nelson on Quora,