Gtk3: Render a GtkHeaderBar as the background of the tab strip

chrome/browser/ui/libgtkui/native_theme_gtk3.h

Index: chrome/browser/ui/libgtkui/native_theme_gtk3.h
diff --git a/chrome/browser/ui/libgtkui/native_theme_gtk3.h b/chrome/browser/ui/libgtkui/native_theme_gtk3.h
index 577375ce1bb4a5f24fda835400c9573e00a2e765..1946f72bb26d4c7f653792d1a77dd8dfc3d10bbb 100644
--- a/chrome/browser/ui/libgtkui/native_theme_gtk3.h
+++ b/chrome/browser/ui/libgtkui/native_theme_gtk3.h
@@ -30,6 +30,11 @@ class NativeThemeGtk3 : public ui::NativeThemeBase {
       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();