Provide lazy CommitPendingWrites in addition to eager SavePersistentPrefs.

chrome/browser/prefs/pref_service.h

Index: chrome/browser/prefs/pref_service.h
diff --git a/chrome/browser/prefs/pref_service.h b/chrome/browser/prefs/pref_service.h
index 2ab7b96d4e7756d384c0f39f8d4fa3fde3e276cf..5ca24fd5ad9ef8ec31cade550e1fa37371d7a2a3 100644
--- a/chrome/browser/prefs/pref_service.h
+++ b/chrome/browser/prefs/pref_service.h
@@ -148,6 +148,9 @@ class PrefService : public base::NonThreadSafe {
   // Serializes the data and schedules save using ImportantFileWriter.
   void ScheduleSavePersistentPrefs();
 
+  // Lands pending writes to disk.
+  void CommitPendingWrite();
+
   // Make the PrefService aware of a pref.
   void RegisterBooleanPref(const char* path, bool default_value);
   void RegisterIntegerPref(const char* path, int default_value);