Removes SimpleMenuModel::FlipIndex. It was only used by

chrome/browser/ui/views/frame/system_menu_model.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/ui/views/frame/system_menu_model.h"
 
 #include <windows.h>
 
 #include <algorithm>
 
 SystemMenuModel::SystemMenuModel(ui::SimpleMenuModel::Delegate* delegate)
     : ui::SimpleMenuModel(delegate) {
 }
 
 SystemMenuModel::~SystemMenuModel() {
 }
 
 int SystemMenuModel::GetFirstItemIndex(gfx::NativeMenu native_menu) const {
   // We allow insertions before last item (Close).
   return std::max(0, GetMenuItemCount(native_menu) - 1);
 }
-
-int SystemMenuModel::FlipIndex(int index) const {
-  return GetItemCount() - index - 1;
-}