After I got the new experimental "Twiggy" pipeline up and running I decided to give Google Native Client another shot, since Twiggy works much better with the "call-on-main-thread" restriction of NaCl. The NaCl port now only differs by a couple of hundred lines of code from the other platform ports which I'm very happy with.
Here's the link to the demo in the Chrome Web Store. You need a recent version of Chrome (at least v.21). So far I only tested this on my MacBook with an nVidia 9400M GPU under OSX and Windows:
If it doesn't work for you, please leave feedback in the Chrome Web Store, especially which GPU you're using.