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

mojo/services/authentication/interfaces/authentication.mojom

Index: mojo/services/authentication/interfaces/authentication.mojom
diff --git a/mojo/services/authentication/interfaces/authentication.mojom b/mojo/services/authentication/interfaces/authentication.mojom
index 235669ec2cf22b82c15f266f0342ec6674b4e0d8..cc2a6f8a58fcf0667b1fa9e37c15f657f29a8839 100644
--- a/mojo/services/authentication/interfaces/authentication.mojom
+++ b/mojo/services/authentication/interfaces/authentication.mojom
@@ -8,6 +8,7 @@ module authentication;
 // Interface to handle user identity and authentication tokens.
 // TODO(qsr): This API only handles google accounts at this time. It will need
 //            to be extended to allow generic account manager on the platform.
+[ServiceName="authentication::AuthenticationService"]
 interface AuthenticationService {
   // Requests a Google account to use. In case of success, error will be null.
   // In case of error, username will be null and error will contain a