not much info is available from the company right now, but this seems like they're using opengl + mono + google's native client[1] extension (enabled by default in current versions of chrome). this is a huge step for mainstream NaCl adoption + quality games/apps. it couldn't be easier to get native speeds for your app without having to cross your fingers V8 compiles your javascript efficiently.

[1] NaCl: https://developers.google.com/native-client/