[Sync] Refactored ProfileSyncService and remove its backend() function

chrome/browser/sync/glue/preference_model_associator.h

 // Copyright (c) 2010 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_SYNC_GLUE_PREFERENCE_MODEL_ASSOCIATOR_H_
 #define CHROME_BROWSER_SYNC_GLUE_PREFERENCE_MODEL_ASSOCIATOR_H_
 #pragma once
 
 #include <map>
 #include <set>
@@ skipping 91 matching lines @@
   // Writes the value of pref into the specified node.  Returns true
   // upon success.
   static bool WritePreferenceToNode(const std::string& name,
                                     const Value& value,
                                     sync_api::WriteNode* node);
 
   // Perform any additional operations that need to happen after a preference
   // has been updated.
   void AfterUpdateOperations(const std::string& pref_name);
 
- protected:
-  // Returns sync service instance.
-  ProfileSyncService* sync_service() { return sync_service_; }
-
  private:
   typedef std::map<std::string, int64> PreferenceNameToSyncIdMap;
   typedef std::map<int64, std::string> SyncIdToPreferenceNameMap;
 
   static Value* MergeListValues(const Value& from_value, const Value& to_value);
   static Value* MergeDictionaryValues(const Value& from_value,
                                       const Value& to_value);
 
   ProfileSyncService* sync_service_;
   std::set<std::string> synced_preferences_;
   int64 preferences_node_id_;
 
   PreferenceNameToSyncIdMap id_map_;
   SyncIdToPreferenceNameMap id_map_inverse_;
 
   DISALLOW_COPY_AND_ASSIGN(PreferenceModelAssociator);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_PREFERENCE_MODEL_ASSOCIATOR_H_