Called as a hint to indicate a new transaction for the URI is likely coming
soon. The implementer may use this information to start a TCP
and/or SSL level handshake for that resource immediately so that it is
ready and/or progressed when the transaction is actually submitted.
No obligation is taken on by the implementer, nor is the submitter obligated
to actually open the new channel.
| aURI | the URI of the hinted transaction |
| aCallbacks | any security callbacks for use with SSL for interfaces such as nsIBadCertListener. May be null. |