Created attachment 651059 [details]
Asserts in an x86_64 Ion debug browser by visiting http://lights.elliegoulding.com, waiting for it to load, and clicking "Play".
The problem is most likely that visitCallDOMNative() is missing a call to dropArguments().
Created attachment 651065 [details] [diff] [review]
Fixes crash. Site runs happily if jankily.