code: function onPushNotificationRegistration(response) {
      if (resolveRegistrationEventResponse) {
          diag.debug.assert(!!rejectRegistrationEventResponse);
          resolveRegistrationEventResponse(response);
          resolveRegistrationEventResponse = undefined;
          rejectRegistrationEventResponse = undefined;
      }
      else {
          promiseRegistrationEventResponse = Q.resolve(response);
      }
      return promiseRegistrationEventResponse.done();
  }
docs: executed when registration at 3rd party push server succeeded and a registration was issued, or a registration is renewed meaning this may be called several times.