Bug 1539694 - Part 3: Update xray tests for Promise. r=peterv

Differential Revision: https://phabricator.services.mozilla.com/D26144

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

js/xpconnect/tests/chrome/test_xrayToJS.xul

@@ -254,6 +254,9 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=933681
     ["constructor", "catch", "then", "finally", Symbol.toStringTag];
   gConstructorProperties['Promise'] =
     constructorProps(["resolve", "reject", "all", "race", Symbol.species]);
+  if (isNightlyBuild) {
+    gConstructorProperties['Promise'].push("allSettled");
+  }
 
   gPrototypeProperties['ArrayBuffer'] =
     ["constructor", "byteLength", "slice", Symbol.toStringTag];