This does not represent the finalized form for a lot of the entries in the snapshot since some types are still not handled, but this at least lets us exercise the code paths and ensure future additions don't change the representations of any existing covered types. I would also like to move the serialization code here into a module we can include from Firefox and the profiler frontend but that's for a future patch. Differential Revision: https://phabricator.services.mozilla.com/D253219