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

mojo/services/terminal/interfaces/terminal_client.mojom

 // Copyright 2015 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.terminal;
 
 import "files/interfaces/file.mojom";
 
 // Interface for applications that want to be able to be connected to by a
 // terminal. (Once connected, such an application will be able to write to/read
 // from the terminal by performing the corresponding operations on the provided
 // "file".)
+[ServiceName="mojo::terminal::TerminalClient"]
 interface TerminalClient {
   ConnectToTerminal(mojo.files.File terminal);
 };