Disabled EnableStartupTracing for Renderer process.

content/app/content_main_runner.cc

 // Copyright (c) 2012 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.
 
 #include "content/public/app/content_main_runner.h"
 
 #include <stdlib.h>
 
 #include "base/allocator/allocator_extension.h"
 #include "base/at_exit.h"
@@ skipping 614 matching lines @@
 
     // Enable startup tracing asap to avoid early TRACE_EVENT calls being
     // ignored.
     if (command_line.HasSwitch(switches::kTraceStartup)) {
       base::trace_event::TraceConfig trace_config(
           command_line.GetSwitchValueASCII(switches::kTraceStartup),
           base::trace_event::RECORD_UNTIL_FULL);
       base::trace_event::TraceLog::GetInstance()->SetEnabled(
           trace_config,
           base::trace_event::TraceLog::RECORDING_MODE);
-    } else if (process_type != switches::kZygoteProcess) {
+    } else if (process_type != switches::kZygoteProcess &&
+               process_type != switches::kRendererProcess) {
       // There is no need to schedule stopping tracing in this case. Telemetry
       // will stop tracing on demand later.

[Zhen Wang, 2015/07/01 00:41:43]

Can you add some comment here to explain why it is ok to skip renderer process
here? Something like:

When ChildTraceMessageFilter is added, Renderer process will start tracing
automatically if tracing is already started in Browser process. 

       tracing::EnableStartupTracingIfConfigFileExists();
     }
 
 #if defined(OS_WIN)
     // Enable exporting of events to ETW if requested on the command line.
     if (command_line.HasSwitch(switches::kTraceExportEventsToETW))
       base::trace_event::TraceEventETWExport::EnableETWExport();
 #endif  // OS_WIN
 
 #if !defined(OS_ANDROID)
@@ skipping 219 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(ContentMainRunnerImpl);
 };
 
 // static
 ContentMainRunner* ContentMainRunner::Create() {
   return new ContentMainRunnerImpl();
 }
 
 }  // namespace content