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

mojo/services/navigation/interfaces/navigation.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.
 
 [DartPackage="mojo_services"]
 module mojo;
 
 import "mojo/public/interfaces/network/url_request.mojom";
 
 // Expresses a preference for where a navigation will be performed.
 enum Target {
   // No preference
   DEFAULT,
 
   // In the same ViewManager node that the navigation was initiated
   SOURCE_NODE,
 
   // In a new ViewManager node
   NEW_NODE
 };
 
 // Embedders that support navigation of implement this interface.
+[ServiceName="mojo::NavigatorHost"]
 interface NavigatorHost {
   RequestNavigate(Target target, URLRequest request);
   RequestNavigateHistory(int32 delta);
 
   // Applications call this to inform hosts of navigations they performed
   // locally. For example, pushState() navigations in an HTML application.
   DidNavigateLocally(string url);
 };