Remove JsonPrefStore pruning of empty values on write.

chrome/browser/prefs/pref_metrics_service.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 CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
 #define CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
 
 #include <map>
 #include <string>
 
@@ skipping 77 matching lines @@
                             const Value* value);
 
   // Callback for an integer pref change histogram.
   void LogIntegerPrefChange(int boundary_value,
                             const std::string& histogram_name,
                             const Value* value);
 
   // Callback to receive a unique device_id.
   void GetDeviceIdCallback(const std::string& device_id);
 
-  // Marks all tracked preferences as required to save their values even if
-  // empty.
-  void MarkNeedsEmptyValueForTrackedPreferences();
-
   // Checks the tracked preferences against their last known values and reports
   // any discrepancies. This must be called after |device_id| has been set.
   void CheckTrackedPreferences();
 
   // Updates the hash of the tracked preference in local state. This must be
   // called after |device_id| has been set.
   void UpdateTrackedPreference(const char* path);
 
   // Computes an MD5 hash for the given preference value. |value| can be
   // NULL which will result in the unique hash representing NULL for the pref
@@ skipping 20 matching lines @@
 
   PrefChangeRegistrar pref_registrar_;
   scoped_ptr<SyncedPrefChangeRegistrar> synced_pref_change_registrar_;
 
   base::WeakPtrFactory<PrefMetricsService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefMetricsService);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_