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

chrome/browser/sync/glue/bookmark_model_associator.h

Index: chrome/browser/sync/glue/bookmark_model_associator.h
diff --git a/chrome/browser/sync/glue/bookmark_model_associator.h b/chrome/browser/sync/glue/bookmark_model_associator.h
index 577979f51b8e07ea5b115ac46c233762c6476e5b..035f684bb484801f15641b691f60e8d4cb599dc2 100644
--- a/chrome/browser/sync/glue/bookmark_model_associator.h
+++ b/chrome/browser/sync/glue/bookmark_model_associator.h
@@ -83,15 +83,15 @@ class BookmarkModelAssociator
     // thread.
   }
 
-  // Returns sync service instance.
-  ProfileSyncService* sync_service() { return sync_service_; }
-
  protected:
   // Stores the id of the node with the given tag in |sync_id|.
   // Returns of that node was found successfully.
   // Tests override this.
   virtual bool GetSyncIdForTaggedNode(const std::string& tag, int64* sync_id);
 
+  // Used by TestBookmarkModelAssociator.
+  ProfileSyncService* sync_service() { return sync_service_; }
+
  private:
   typedef std::map<int64, int64> BookmarkIdToSyncIdMap;
   typedef std::map<int64, const BookmarkNode*> SyncIdToBookmarkNodeMap;