LibGtkUi: Partition NativeThemeGtk into NativeThemeGtk2 and NativeThemeGtk3

chrome/browser/ui/libgtkui/native_theme_gtk2.h

 // Copyright (c) 2013 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 CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK_H_
-#define CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK_H_
-
-#include <gtk/gtk.h>
+#ifndef CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK2_H_
+#define CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK2_H_
 
 #include "base/macros.h"
 #include "ui/native_theme/native_theme_base.h"
 
+typedef struct _GtkWidget GtkWidget;
+
 namespace libgtkui {
 
 // A version of NativeTheme that uses GTK2 supplied colours instead of the
 // default aura colours. Analogue to NativeThemeWin, except that can't be
 // compiled into the main chrome binary like the Windows code can.
 class NativeThemeGtk2 : public ui::NativeThemeBase {
  public:
   static NativeThemeGtk2* instance();
 
   // Overridden from ui::NativeThemeBase:
   SkColor GetSystemColor(ColorId color_id) const override;
   void PaintMenuPopupBackground(
       SkCanvas* canvas,
       const gfx::Size& size,
       const MenuBackgroundExtraParams& menu_background) const override;
   void PaintMenuItemBackground(
       SkCanvas* canvas,
       State state,
       const gfx::Rect& rect,
       const MenuItemExtraParams& menu_item) const override;
 
-  // Gets a ChromeGtkFrame theme color; returns true on success. Always returns
-  // false in GTK3.
-  bool GetChromeStyleColor(const char* style_property,
-                           SkColor* ret_color) const;
+ private:
+  NativeThemeGtk2();
+  ~NativeThemeGtk2() override;
 
   // Returns various widgets for theming use.
   GtkWidget* GetWindow() const;
   GtkWidget* GetEntry() const;
   GtkWidget* GetLabel() const;
   GtkWidget* GetButton() const;
   GtkWidget* GetBlueButton() const;
   GtkWidget* GetTree() const;
   GtkWidget* GetTooltip() const;
   GtkWidget* GetMenu() const;
   GtkWidget* GetMenuItem() const;
 
- private:
-  NativeThemeGtk2();
-  ~NativeThemeGtk2() override;
-
   DISALLOW_COPY_AND_ASSIGN(NativeThemeGtk2);
 };
 
 }  // namespace libgtkui
 
-#endif  // CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK_H_
+#endif  // CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK2_H_