Require an explicit ServiceName annotation for interfaces in C++.

services/test_service/test_service.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mojo.test;
 
+[ServiceName="mojo::test::TestService"]
 interface TestService {
   Ping() => ();
   // Connect to a TestTimeService at |app_url| and ferry the data back
   // in |response|.
   ConnectToAppAndGetTime(string? app_url) => (int64 time_usec);
   StartTrackingRequests() => ();
 };
 
+[ServiceName="mojo::test::TestTimeService"]
 interface TestTimeService {
   // Provides a constant time value.
   GetPartyTime() => (int64 time_usec);
   StartTrackingRequests() => ();
 };