Bug 1519399 - Fix browser_parsable_css.js for scroll-anchoring as it's behind a pref. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D16404

--HG--
extra : moz-landing-system : lando

browser/base/content/test/static/browser_parsable_css.js

@@ -95,6 +95,14 @@ if (!Services.prefs.getBoolPref("layout.css.scrollbar-width.enabled")) {
   });
 }
 
+if (!Services.prefs.getBoolPref("layout.css.scroll-anchoring.enabled")) {
+  whitelist.push({
+    sourceName: /webconsole\.css$/i,
+    errorMessage: /Unknown property .*\boverflow-anchor\b/i,
+    isFromDevTools: true,
+  });
+}
+
 let propNameWhitelist = [
   // These custom properties are retrieved directly from CSSOM
   // in videocontrols.xml to get pre-defined style instead of computed