Completed the challenge.  Added the notification (see attached image) in the Wave developer org.  It looks like it did not save the first time.  Added the notification a 2nd time, as shown in screen capture. 

1) I used use Module3RegistrationHandler.cls as registration handler.
2) I selected Google as login capability for Partners ( cf screenshot below)
However, the challenge fails with the following message :
Challenge Not yet complete... here's what's wrong:  Could not find a login to your community using Google.
Anybody can help ?
Thanks :-)