MacViews: draw combobox arrow backgrounds

ui/native_theme/native_theme_mac.h

Index: ui/native_theme/native_theme_mac.h
diff --git a/ui/native_theme/native_theme_mac.h b/ui/native_theme/native_theme_mac.h
index 6fe3f61d1c47405df19cfb0d264944203507b706..46d219e82bb0753cea1496011155a74cbb0a78c2 100644
--- a/ui/native_theme/native_theme_mac.h
+++ b/ui/native_theme/native_theme_mac.h
@@ -14,6 +14,8 @@ namespace ui {
 // Mac implementation of native theme support.
 class NATIVE_THEME_EXPORT NativeThemeMac : public NativeThemeBase {
  public:
+  static const int kComboboxCornerRadius = 5;
+
   static NativeThemeMac* instance();
 
   // Overridden from NativeTheme:
@@ -30,6 +32,11 @@ class NATIVE_THEME_EXPORT NativeThemeMac : public NativeThemeBase {
       const gfx::Rect& rect,
       const MenuItemExtraParams& menu_item) const override;
 
+  // Creates a shader appropriate for painting the background of a button.
+  static skia::RefPtr<SkShader> GetButtonBackgroundShader(
+      State state,
+      int height);
+
  private:
   NativeThemeMac();
   ~NativeThemeMac() override;