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

mojo/services/tracing/interfaces/tracing.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 tracing;
 
 // To participate in the tracing ecosystem, implement the TraceProvider
 // interface and connect to the tracing app. Then, when the provider's Start()
 // function is called collect tracing data and pass it back via the provided
 // TraceRecorder interface up until Stop() is called.
 
+[ServiceName="tracing::TraceProvider"]
 interface TraceProvider {
   // Categories can either be the empty string to mean the default set of
   // categories or a comma-delimited list of categories to trace.
   StartTracing(string categories, TraceRecorder recorder);
   StopTracing();
 };
 
 interface TraceRecorder {
   Record(string json);
 };
 
+[ServiceName="tracing::TraceCollector"]
 interface TraceCollector {
   // Request tracing data from all connected providers to stream to
   // |stream|.
   Start(handle<data_pipe_producer> stream, string categories);
 
   // Stop tracing and flush results to the |stream| passed in to Start().
   // Closes |stream| when all data is collected.
   StopAndFlush();
 };