Use a direct include of strings headers in ui/, part 3.

ui/views/button_drag_utils.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_VIEWS_BUTTON_DRAG_UTILS_H_
 #define UI_VIEWS_BUTTON_DRAG_UTILS_H_
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/views/views_export.h"
 
 class GURL;
 
 namespace gfx {
 class ImageSkia;
 }
 
 namespace ui {
 class OSExchangeData;
 }
 
 namespace views {
 class Widget;
 }
 
 namespace button_drag_utils {
 
 // Sets url and title on data as well as setting a suitable image for dragging.
 // The image looks like that of the bookmark buttons.
 VIEWS_EXPORT void SetURLAndDragImage(const GURL& url,
                                      const string16& title,
                                      const gfx::ImageSkia& icon,
                                      ui::OSExchangeData* data,
                                      views::Widget* widget);
 
 }  // namespace drag_utils
 
 #endif  // UI_VIEWS_BUTTON_DRAG_UTILS_H_