Provide lazy CommitPendingWrites in addition to eager SavePersistentPrefs.

chrome/browser/prefs/overlay_persistent_pref_store.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PREFS_OVERLAY_PERSISTENT_PREF_STORE_H_
 #define CHROME_BROWSER_PREFS_OVERLAY_PERSISTENT_PREF_STORE_H_
 #pragma once
 
 #include <string>
 
@@ skipping 25 matching lines @@
   virtual ReadResult GetValue(const std::string& key, Value** result) const;
 
   // Methods of PersistentPrefStore.
   virtual void SetValue(const std::string& key, Value* value);
   virtual void SetValueSilently(const std::string& key, Value* value);
   virtual void RemoveValue(const std::string& key);
   virtual bool ReadOnly() const;
   virtual PrefReadError ReadPrefs();
   virtual bool WritePrefs();
   virtual void ScheduleWritePrefs();
+  virtual void CommitPendingWrite();
   // TODO(battre) remove this function
   virtual void ReportValueChanged(const std::string& key);
 
  private:
   // Methods of PrefStore::Observer.
   virtual void OnPrefValueChanged(const std::string& key);
   virtual void OnInitializationCompleted();
 
   ObserverList<PrefStore::Observer, true> observers_;
   PrefValueMap overlay_;
   scoped_refptr<PersistentPrefStore> underlay_;
 
   DISALLOW_COPY_AND_ASSIGN(OverlayPersistentPrefStore);
 };
 
 #endif  // CHROME_BROWSER_PREFS_OVERLAY_PERSISTENT_PREF_STORE_H_