Use a direct include of strings headers in ui/, part 2.

ui/base/models/simple_menu_model.h

 // 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.
 
 #ifndef UI_BASE_MODELS_SIMPLE_MENU_MODEL_H_
 #define UI_BASE_MODELS_SIMPLE_MENU_MODEL_H_
 
 #include <vector>
 
 #include "base/memory/weak_ptr.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/base/models/menu_model.h"
 
 namespace gfx {
 class Image;
 }
 
 namespace ui {
 
 class ButtonMenuItemModel;
 
@@ skipping 157 matching lines @@
   MenuModelDelegate* menu_model_delegate_;
 
   base::WeakPtrFactory<SimpleMenuModel> method_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SimpleMenuModel);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_MODELS_SIMPLE_MENU_MODEL_H_