Add CrossOriginConnectEvent and CrossOriginServiceWorkerClient objects.
Add CrossOriginConnectEvent and CrossOriginServiceWorkerClient objects.

This change adds the appropriate prototypes so that the object passed to
the 'crossoriginconnect' event handler has a 'client' field that
contains a proper CrossOriginServiceWorkerClient object to match the spec.

This client object is not yet set as the source for 'crossoriginmessage'
events.

mkruisselbrink/navigator-connect,mkruisselbrink/navigator-connect