Provide lazy CommitPendingWrites in addition to eager SavePersistentPrefs.

chrome/browser/prefs/pref_service.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.
 
 // This provides a way to access the application's current preferences.
 
 #ifndef CHROME_BROWSER_PREFS_PREF_SERVICE_H_
 #define CHROME_BROWSER_PREFS_PREF_SERVICE_H_
 #pragma once
 
@@ skipping 130 matching lines @@
   // Writes the data to disk. The return value only reflects whether
   // serialization was successful; we don't know whether the data actually made
   // it on disk (since it's on a different thread).  This should only be used if
   // we need to save immediately (basically, during shutdown).  Otherwise, you
   // should use ScheduleSavePersistentPrefs.
   bool SavePersistentPrefs();
 
   // 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);
   void RegisterDoublePref(const char* path, double default_value);
   void RegisterStringPref(const char* path, const std::string& default_value);
   void RegisterFilePathPref(const char* path, const FilePath& default_value);
   void RegisterListPref(const char* path);
   void RegisterDictionaryPref(const char* path);
   // These take ownership of the default_value:
   void RegisterListPref(const char* path, ListValue* default_value);
@@ skipping 156 matching lines @@
 
   // Local cache of registered Preference objects. The default_store_
   // is authoritative with respect to what the types and default values
   // of registered preferences are.
   mutable PreferenceSet prefs_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefService);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_SERVICE_H_