Add tracing to prefs for analyzing startup performance

chrome/browser/prefs/pref_service_syncable_builder.cc

Index: chrome/browser/prefs/pref_service_syncable_builder.cc
diff --git a/chrome/browser/prefs/pref_service_syncable_builder.cc b/chrome/browser/prefs/pref_service_syncable_builder.cc
index e5b464a69e20bb72f87cd9461b8648e08e8dd852..c8214dbdf9b8252afaeb08e1599bf8508418b5a9 100644
--- a/chrome/browser/prefs/pref_service_syncable_builder.cc
+++ b/chrome/browser/prefs/pref_service_syncable_builder.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/prefs/pref_service_syncable_builder.h"
 
+#include "base/debug/trace_event.h"
 #include "base/prefs/default_pref_store.h"
 #include "base/prefs/pref_notifier_impl.h"
 #include "base/prefs/pref_value_store.h"
@@ -43,6 +44,7 @@ PrefServiceSyncableBuilder::WithCommandLine(CommandLine* command_line) {
 
 PrefServiceSyncable* PrefServiceSyncableBuilder::CreateSyncable(
     user_prefs::PrefRegistrySyncable* pref_registry) {
+  TRACE_EVENT0("browser", "PrefServiceSyncableBuilder::CreateSyncable")
   PrefNotifierImpl* pref_notifier = new PrefNotifierImpl();
   PrefServiceSyncable* pref_service = new PrefServiceSyncable(
       pref_notifier,