Re: [webcomponents] Change registries to be per document and never shared between documents (#369)

So it turns out that we can't share the registry in option 1 because `ownerDocument` would need to be `window.document` initially and this is observable in custom elements constructor.  So I think we need to disallow custom elements in window-less documents.

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/369#issuecomment-191972731