macviews: honor system control tint setting

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 f87d87fa69122fc259b6dc95948a113844caf810..ec48119d26442030155d1a14ee8235f45d4becfb 100644
--- a/ui/native_theme/native_theme_mac.h
+++ b/ui/native_theme/native_theme_mac.h
@@ -29,6 +29,11 @@ class NATIVE_THEME_EXPORT NativeThemeMac : public NativeThemeBase {
 
   static NativeThemeMac* instance();
 
+  // Adjusts an SkColor based on the current system control tint. For example,
+  // if the current tint is "graphite", this function maps the provided value to
+  // an appropriate gray.
+  static SkColor ApplySystemControlTint(SkColor color);
+
   // Overridden from NativeTheme:
   SkColor GetSystemColor(ColorId color_id) const override;