[Startup Tracing] Enable startup tracing from config file

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 7f99d7c8c8c3bee44a159597eab67bc5b8d552c6..45e4028f58acaccc5696cf1fb229533ddaf4a293 100644
--- a/mandoline/app/desktop/launcher_process.cc
+++ b/mandoline/app/desktop/launcher_process.cc
@@ -88,6 +88,8 @@ int LauncherProcessMain(int argc, char** argv) {
         base::trace_event::RECORD_UNTIL_FULL);
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
         trace_config, base::trace_event::TraceLog::RECORDING_MODE);
+  } else {
+    base::trace_event::EnableStartupTracingIfConfigFileExists();
   }
 
   // We want the runner::Context to outlive the MessageLoop so that pipes are