It doesn't run by default. But remember it's Google who's pushing this, and their browser has momentum. I'd guess it's just a matter of time before they run it by default. They already cashed out for security bounties for NaCl in the past[1] and seem to have increased resources recently[2] since it's quite a lucrative market for gaming.

[1] https://developers.google.com/native-client/community/securi... [2] m.yahoo.com/w/legobpengine/news/google-bringing-high-end-gaming-chrome-via-native-054102268.html