Migrate startActivityForResult/onActivityResult to
StartActivityForResult/registerForActivityResult in
LoginActivity/OAuth.
This moves responsibility for scheduling the starting Intent from
OAuth to LoginActivity.
OAuth still generates the Intent. But instead of starting the intent
directly in OAuth, the intent is returned to LoginActivity. This
better associates processing the activity result with its invocation.
OAuthTest module updated to accommodate internal API change.
Ryan Harg
Hugh Daschbach
Ryan Harg