Sets @site_for_cookies as the policy URL for same-site cookies for @msg.
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.
Sets @site_for_cookies as the policy URL for same-site cookies for @msg.
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 for more information.