Integrate registry_hash_store_contents with the rest of tracked prefs.

components/prefs/pref_filter.h

 // Copyright 2013 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 COMPONENTS_PREFS_PREF_FILTER_H_
 #define COMPONENTS_PREFS_PREF_FILTER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 33 matching lines @@
   // Receives notification when a pref store value is changed, before Observers
   // are notified.
   virtual void FilterUpdate(const std::string& path) = 0;
 
   // Receives notification when the pref store is about to serialize data
   // contained in |pref_store_contents| to a string. Modifications to
   // |pref_store_contents| will be persisted to disk and also affect the
   // in-memory state.
   virtual void FilterSerializeData(
       base::DictionaryValue* pref_store_contents) = 0;
+
+  // Returns a callback which should be called once the pref_store is written.
+  virtual base::Closure GetPostSerializeCallback(
+      base::DictionaryValue* pref_store_contents) = 0;

[gab, 2016/08/03 18:19:34]

Instead of forcing the caller to call this in a particular order w.r.t.
FilterSerializeData, make the API:

  // Receives notification when the pref store is about to serialize data
  // contained in |pref_store_contents| to a string. Modifications to
  // |pref_store_contents| will be persisted to disk and also affect the
  // in-memory state. If the returned Callback is non-null, it will be
  // registered to be invoked synchronously after the next write (from the I/O
  // TaskRunner so it must not be bound to thread-unsafe member state).
  virtual base::Callback<void(bool success)> FilterSerializeData(
      base::DictionaryValue* pref_store_contents) = 0;

then it's up to the implementation to do things in the order that pleases it.

[proberge, 2016/08/04 00:13:45]

Done.

 };
 
 #endif  // COMPONENTS_PREFS_PREF_FILTER_H_