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

shell/application_manager/test.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 shell;
 
+[ServiceName="shell::TestService"]
 interface TestService {
   Test(string test_string) => ();
 };
 
+[ServiceName="shell::TestA"]
 interface TestA {
   CallB();
   CallCFromB();
 };
 
+[ServiceName="shell::TestB"]
 interface TestB {
   B() => ();
   CallC() => ();
 };
 
+[ServiceName="shell::TestC"]
 interface TestC {
   C() => ();
 };