Bug 1705168: Enable forced-colors in UA and chrome always r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D112069

layout/style/test/chrome/test_chrome_only_media_queries.html

@@ -6,6 +6,25 @@
 <script>
 const SHEET = document.querySelector('style');
 
+SimpleTest.waitForExplicitFinish();
+
+async function testWithPref() {
+  await new Promise(r => {
+    SpecialPowers.pushPrefEnv(
+      {
+        set: [
+          ["layout.css.forced-colors.enabled", false],
+        ],
+      },
+      r
+    );
+  });
+  expectParseable("(forced-colors: none)");
+  expectParseable("(forced-colors: active)");
+  expectParseable("(forced-colors)");
+  SimpleTest.finish();
+}
+
 function expect(q, shouldBeParseable) {
   const NOT_PARSEABLE_TEXT = "@media screen, not all {\n}";
 
@@ -63,5 +82,11 @@ expectParseable("(prefers-contrast: no-preference)")
 expectParseable("(prefers-contrast: less)");
 expectParseable("(prefers-contrast)")
 
+expectParseable("(forced-colors: none)");
+expectParseable("(forced-colors: active)");
+expectParseable("(forced-colors)");
+
 expectNonParseable("(-moz-os-version: )");
+
+testWithPref();
 </script>

servo/components/style/media_queries/media_feature_expression.rs

@@ -221,7 +221,11 @@ fn disabled_by_pref(feature: &Atom, context: &ParserContext) -> bool {
     #[cfg(feature = "gecko")]
     {
         if *feature == atom!("forced-colors") {
-            return !static_prefs::pref!("layout.css.forced-colors.enabled");
+            // forced-colors is always enabled in the ua and chrome. On
+            // the web it is hidden behind a preference, which is defaulted
+            // to 'true' as of bug 1659511.
+            return !context.in_ua_or_chrome_sheet() &&
+                !static_prefs::pref!("layout.css.forced-colors.enabled");
         }
         // prefers-contrast is always enabled in the ua and chrome. On
         // the web it is hidden behind a preference.