Make tracing work on Android

services/tracing/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.
 
 module tracing;
 
 // To particate in the tracing ecosystem, implement the TraceController
 // interface and connect to the tracing app. Then, when the controller's Start()
 // function is called collect tracing data and pass it back via the
 // TraceDataCollector interface up until Stop() is called.
 
 [Client=TraceDataCollector]
 interface TraceController {
   StartTracing(string categories);
   StopTracing();
 };
 
 [Client=TraceController]
 interface TraceDataCollector {
   DataCollected(string json);
   EndTracing();
 };
 
 interface TraceCoordinator {
-  // Request tracing data from all connected TraceControllers to save in a file
-  // derived from |base_name|.
-  Start(string base_name, string categories);
+  // Request tracing data from all connected TraceControllers to stream to
+  // |stream|.
+  Start(handle<data_pipe_producer> stream, string categories);
 
   // Stop tracing and flush results to file.
   StopAndFlush();
 };