Code review comment for lp:~vanvugt/mir/predictive-bypass-2

If it makes people feel better I can propose the Mesa implementation first (which is safer in theory) and Android second. They're completely independent. But in my mind both are finished.

As for sleeping and safety, I added the environment variables late in the game as a safety net (and also as a testing tool) so you can evaluate the benefits in production. Especially if you suspect that turning off predictive bypass will help you; you can test that theory with MIR_DRIVER_FORCE_BYPASS_SLEEP=0. (better variable name?)

Yes, it's possible future devices will require additional tweaks to avoid skipping frames, but unlikely. I find it difficult to believe we'll encounter any device that is slower than arale (which seems to require 6ms just to post a frame without any GL rendering).