They don't. Many Google developers use customised versions of Linux, but that's it.
None.
Then why are you saying
Google developers already use the google OS as their main setup because it's the best[source needed]
...?
I said I seem to remember reading that on engadget but can no longer find the source and I already admitted that. The real mystery is what are you trying to say?
Does Syphon work for Google? lol
None.