style: Make color-scheme affect Windows' non-native menus

This matches what Linux and macOS do, and that allows the fix for bug 1782623
to work on Windows for unstyled selects.

This also simplifies the CSS (though it adds a new system color which is a bit
more annoying). I filed w3c/csswg-drafts#7561 to
propose adding a more generic way to do this in the future (not just for
Firefox).

Differential Revision: https://phabricator.services.mozilla.com/D153549

components/style/gecko/media_features.rs

@@ -496,18 +496,8 @@ fn eval_moz_platform(_: &Context, query_value: Option<Platform>) -> bool {
     unsafe { bindings::Gecko_MediaFeatures_MatchesPlatform(query_value) }
 }
 
-fn eval_moz_windows_non_native_menus(context: &Context) -> bool {
-    let use_non_native_menus = match static_prefs::pref!("browser.display.windows.non_native_menus")
-    {
-        0 => false,
-        1 => true,
-        _ => {
-            eval_moz_platform(context, Some(Platform::WindowsWin10)) &&
-                get_lnf_int_as_bool(bindings::LookAndFeel_IntID::WindowsDefaultTheme as i32)
-        },
-    };
-
-    use_non_native_menus
+fn eval_moz_windows_non_native_menus(_: &Context) -> bool {
+    unsafe { bindings::Gecko_MediaFeatures_WindowsNonNativeMenus() }
 }
 
 fn eval_moz_overlay_scrollbars(context: &Context) -> bool {

components/style/values/specified/color.rs

@@ -198,6 +198,9 @@ pub enum SystemColor {
     MozButtonhovertext,
     /// Used for menu item backgrounds when hovered.
     MozMenuhover,
+    /// Used for menu item backgrounds when hovered and disabled.
+    #[parse(condition = "ParserContext::in_ua_or_chrome_sheet")]
+    MozMenuhoverdisabled,
     /// Used for menu item text when hovered.
     MozMenuhovertext,
     /// Used for menubar item text.