It's not clear to me how this could ever be anything sane except the compartment principals. I think we should remove it, unless anyone knows something that I don't. We probably need to keep originPrincipals for now, though.

Sounds good. Perhaps we can assert, on script creation, that whatever principle was passed is equivalent to compartment->principle?

This is a pretty conservative patch. Once we've given the assertions some time, we'll be able to remove more code. I left the field in as padding, but I'm planning to use it for zones pretty soon. https://tbpl.mozilla.org/?tree=Try&rev=d9ddc605aa59