We cannot request new permissions when Dialer UI is shown. For incoming
calls, if the Dialer UI is displayed over keyguard, then the user may
not even be able to see the permission notifications that we use for
outgoing calls.
If we just do not use the Dialer UI when the permission is not granted,
it is at most a minor annoyance for the first time. After the user has
accepted an incoming call even just once, the permission will be
granted, and the Dialer integration will start to work just fine.
