public void set_site_for_cookies (URI? site_for_cookies)
site_for_cookies as the policy URL for same-site cookies for this.
It is either the URL of the top-level document or
null depending on whether the registrable domain of this document's URL matches
the registrable domain of its parent's/opener's URL. For the top-level document it is set to the document's URL.
See the [same-site spec](https://tools.ietf.org/html/draft-ietf-httpbis-cookie-same-site-00) for more information.
the URI for the this's site for cookies