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

ui/views/controls/button/checkbox.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_CONTROLS_BUTTON_CHECKBOX_H_
 #define UI_VIEWS_CONTROLS_BUTTON_CHECKBOX_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/views/controls/button/label_button.h"
 
 namespace views {
 
 // A native themed class representing a checkbox.  This class does not use
 // platform specific objects to replicate the native platforms looks and feel.
 class VIEWS_EXPORT Checkbox : public LabelButton {
  public:
   static const char kViewClassName[];
 
@@ skipping 37 matching lines @@
 
   // The images for each button state.
   gfx::ImageSkia images_[2][2][STATE_COUNT];
 
   DISALLOW_COPY_AND_ASSIGN(Checkbox);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_BUTTON_CHECKBOX_H_