ui: Move NativeTheme files into ui/base/native_theme/ directory.

ui/gfx/native_theme_gtk.h

Index: ui/gfx/native_theme_gtk.h
diff --git a/ui/gfx/native_theme_gtk.h b/ui/gfx/native_theme_gtk.h
deleted file mode 100644
index 2fb205cc5e97dcac160fc4479b4577136e0b92e7..0000000000000000000000000000000000000000
--- a/ui/gfx/native_theme_gtk.h
+++ /dev/null
@@ -1,27 +0,0 @@
-// Copyright (c) 2011 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_GFX_NATIVE_THEME_GTK_H_
-#define UI_GFX_NATIVE_THEME_GTK_H_
-#pragma once
-
-#include "ui/gfx/native_theme_base.h"
-
-namespace gfx {
-
-// GTK implementation of native theme support.
-class NativeThemeGtk : public NativeThemeBase {
- public:
-  static const NativeThemeGtk* instance();
-
-  virtual SkColor GetSystemColor(ColorId color_id) const OVERRIDE;
-
- private:
-  NativeThemeGtk();
-  virtual ~NativeThemeGtk();
-};
-
-}  // namespace gfx
-
-#endif  // UI_GFX_NATIVE_THEME_GTK_H_