[Startup Tracing] Add --trace-config-file flag

mandoline/app/desktop/launcher_process.cc

Index: mandoline/app/desktop/launcher_process.cc
diff --git a/mandoline/app/desktop/launcher_process.cc b/mandoline/app/desktop/launcher_process.cc
index afa1d15bcb578d77371cdb8297e32c0b063228c6..7b77b6ff903a3763f29e88dc9ce3211256bd5d3a 100644
--- a/mandoline/app/desktop/launcher_process.cc
+++ b/mandoline/app/desktop/launcher_process.cc
@@ -15,7 +15,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/trace_event/trace_event.h"
-#include "components/tracing/startup_tracing.h"
+#include "components/tracing/trace_config_file.h"
 #include "components/tracing/tracing_switches.h"
 #include "mandoline/app/core_services_initialization.h"
 #include "mandoline/app/desktop/launcher_process.h"
@@ -91,9 +91,12 @@ int LauncherProcessMain(int argc, char** argv) {
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
         trace_config, base::trace_event::TraceLog::RECORDING_MODE);
   } else {
-    // |g_tracing| is not touched in this case and Telemetry will stop tracing
-    // on demand later.
-    tracing::EnableStartupTracingIfConfigFileExists();
+    if (tracing::TraceConfigFile::GetInstance()->IsEnabled()) {

[msw, 2015/08/25 18:22:47]

nit: combine with the line above for an "else if". (ditto in mojo)

[Zhen Wang, 2015/08/25 18:54:33]

Done.

+      g_tracing = true;
+      base::trace_event::TraceLog::GetInstance()->SetEnabled(
+          tracing::TraceConfigFile::GetInstance()->GetTraceConfig(),
+          base::trace_event::TraceLog::RECORDING_MODE);
+    }
   }
 
   // We want the runner::Context to outlive the MessageLoop so that pipes are