Get rid of the ability to unregister preferences.

chrome/browser/prefs/pref_model_associator.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/prefs/pref_model_associator.h"
 
 #include "base/auto_reset.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/location.h"
@@ skipping 381 matching lines @@
 
 void PrefModelAssociator::RegisterPref(const char* name) {
   DCHECK(!models_associated_ && registered_preferences_.count(name) == 0);
   registered_preferences_.insert(name);
 }
 
 bool PrefModelAssociator::IsPrefRegistered(const char* name) {
   return registered_preferences_.count(name) > 0;
 }
 
-void PrefModelAssociator::UnregisterPref(const char* name) {
-  DCHECK(synced_preferences_.count(name) == 0);
-  registered_preferences_.erase(name);
-}
-
 void PrefModelAssociator::ProcessPrefChange(const std::string& name) {
   if (processing_syncer_changes_)
     return;  // These are changes originating from us, ignore.
 
   // We only process changes if we've already associated models.
   if (!models_associated_)
     return;
 
   const PrefService::Preference* preference =
       pref_service_->FindPreference(name.c_str());
@@ skipping 34 matching lines @@
   }
 
   syncer::SyncError error =
       sync_processor_->ProcessSyncChanges(FROM_HERE, changes);
 }
 
 void PrefModelAssociator::SetPrefService(PrefServiceSyncable* pref_service) {
   DCHECK(pref_service_ == NULL);
   pref_service_ = pref_service;
 }