Add tracing to prefs for analyzing startup performance

chrome/browser/prefs/browser_prefs.cc

Index: chrome/browser/prefs/browser_prefs.cc
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index acf1321f0723de6bb2e1b82506d2b6811534a0ac..e0f080b8c7d92b0a7a13263d769c4c5a469d80ca 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/prefs/browser_prefs.h"
 
 #include "apps/prefs.h"
+#include "base/debug/trace_event.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/about_flags.h"
@@ -279,6 +280,7 @@ void RegisterLocalState(PrefRegistrySimple* registry) {
 }
 
 void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry) {
+  TRACE_EVENT0("browser", "chrome::RegisterUserPrefs");
   // User prefs. Please keep this list alphabetized.
   AlternateErrorPageTabObserver::RegisterUserPrefs(registry);
   autofill::AutofillDialogControllerImpl::RegisterUserPrefs(registry);