Provide lazy CommitPendingWrites in addition to eager SavePersistentPrefs.

chrome/common/json_pref_store.h

Index: chrome/common/json_pref_store.h
diff --git a/chrome/common/json_pref_store.h b/chrome/common/json_pref_store.h
index d5970b95f948d5a1214319ae9d56eb52ab35ed51..6688f2f5514a2c75a1d59e0c335d1048535a7ae6 100644
--- a/chrome/common/json_pref_store.h
+++ b/chrome/common/json_pref_store.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -29,6 +29,7 @@ class JsonPrefStore : public PersistentPrefStore,
  public:
   // |file_message_loop_proxy| is the MessageLoopProxy for a thread on which
   // file I/O can be done.
+  // |source| is source to be used for sending PREF_COMMMITTED notification.
   JsonPrefStore(const FilePath& pref_filename,
                 base::MessageLoopProxy* file_message_loop_proxy);
   virtual ~JsonPrefStore();
@@ -46,6 +47,8 @@ class JsonPrefStore : public PersistentPrefStore,
   virtual PrefReadError ReadPrefs();
   virtual bool WritePrefs();
   virtual void ScheduleWritePrefs();
+  virtual void CommitPendingWrite();
+  void SetNotificationSource(const NotificationSource& source);

[Mattias Nissler (ping if slow), 2011/03/23 15:12:37]

This is not well-defined. Note that a PrefStore can be hooked up to multiple
PrefServices, thus pushing a source down and sending the notification from there
is not a good idea.

Note that PrefStore already has an observer interface to you could use to
propagate the notification back up. Why not add your stuff there?

We have invested considerable time recently to detangle all Pref classes. One of
the goals was to concentrate sending notifications in PrefNotifierImpl, and your
CL adds back in a notification from deep within the pref system, which we like
to avoid since it decouples the innards of the implementation from the
interface, which is implemented in PrefService.

   // TODO(battre) remove this function
   virtual void ReportValueChanged(const std::string& key);
 
@@ -62,6 +65,9 @@ class JsonPrefStore : public PersistentPrefStore,
   // Helper for safely writing pref data.
   ImportantFileWriter writer_;
 
+  // Source for PREF_COMMITTED notification.
+  NotificationSource source_;
+
   ObserverList<PrefStore::Observer, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);