public void add_cookie_with_first_party (URI first_party, owned Cookie cookie)
cookie to this, emitting the 'changed' signal if we are modifying an existing cookie or
adding a valid new cookie ('valid' means that the cookie's expire date is not in the past).
first_party will be used to reject cookies coming from third party resources in case such a security policy is set in the
cookie will be 'stolen' by the jar, so don't free it afterwards.
For secure cookies to work properly you may want to use add_cookie_full.
the URI for the main document