Disabled EnableStartupTracing for Renderer process.

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index b59c95a6acf3600f4b6793e8a1697355df4e9f72..2906e77f0d2d805215b63bd2a352c525cf788f65 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -632,7 +632,8 @@ class ContentMainRunnerImpl : public ContentMainRunner {
       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();