Port events to transitional syntax, part 2.

I removed the constructor for Event - I haven't yet decided whether constructors should be able to return null, and the existing one can return null. I'm leaning toward "no" here, since it would be nice to have a guarantee that a constructor either returns a valid object or throws.
Nit: if changing these to single-line comments, the */ at the end of the line should be removed too.