Native themes: Add menu separator part

chrome/browser/ui/libgtkui/native_theme_gtk3.h

 // Copyright 2016 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_GTK3_H_
 #define CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK3_H_
 
 #include "base/macros.h"
 #include "base/optional.h"
 #include "ui/native_theme/native_theme_base.h"
 
 namespace libgtkui {
 
 // A version of NativeTheme that uses GTK3-rendered widgets.
 class NativeThemeGtk3 : public ui::NativeThemeBase {
  public:
   static NativeThemeGtk3* instance();
 
   // Called when gtk theme changes.
   void ResetColorCache();
 
   // 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 PaintMenuSeparator(
+      SkCanvas* canvas,
+      State state,
+      const gfx::Rect& rect,
+      const MenuSeparatorExtraParams& menu_separator) const override;
   void PaintMenuItemBackground(
       SkCanvas* canvas,
       State state,
       const gfx::Rect& rect,
       const MenuItemExtraParams& menu_item) const override;
   void PaintFrameTopArea(
       SkCanvas* canvas,
       State state,
       const gfx::Rect& rect,
       const FrameTopAreaExtraParams& frame_top_area) const override;
 
  private:
   NativeThemeGtk3();
   ~NativeThemeGtk3() override;
 
   mutable base::Optional<SkColor> color_cache_[kColorId_NumColors];
 
   DISALLOW_COPY_AND_ASSIGN(NativeThemeGtk3);
 };
 
 }  // namespace libgtkui
 
 #endif  // CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK3_H_