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

ui/views/widget/native_widget_private.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_WIDGET_NATIVE_WIDGET_PRIVATE_H_
 #define UI_VIEWS_WIDGET_NATIVE_WIDGET_PRIVATE_H_
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/ime/input_method_delegate.h"
 #include "ui/views/widget/native_widget.h"
 
 namespace gfx {
 class ImageSkia;
 class Rect;
 }
 
@@ skipping 195 matching lines @@
   virtual ui::NativeTheme* GetNativeTheme() const = 0;
 
   // Overridden from NativeWidget:
   virtual internal::NativeWidgetPrivate* AsNativeWidgetPrivate() OVERRIDE;
 };
 
 }  // namespace internal
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_NATIVE_WIDGET_PRIVATE_H_