For its part, Google was the most unequivocal. Spokesman Aaron Stein e-mailed: "We've never received such a request, but if we did, our response would be simple: 'no way.'"[0]
I wonder if Google could even run a program like this while keeping it secret. Yahoo had their program discovered within weeks, and public within a year. Stamos could easily have immediately gone public in a way which would have prevented him from being prosecuted - say posting a blog post about how hypothetically Yahoo would implement such a system at the governments request, forwarding this on to Bruce Scheiner, and then refusing to comment if such a "hypothetical" program actually existed.
[0] http://arstechnica.com/tech-policy/2016/10/report-fbi-andor-...