Bug 1573590. Make sure we're in the right compartment before serializing our stack in worker error reporting. r=bhackett

Nothing guarantees that the current compartment of aCx matches the compartment
where the exception was thrown.

Differential Revision: https://phabricator.services.mozilla.com/D41791

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

dom/workers/WorkerPrivate.cpp

@@ -4134,6 +4134,7 @@ void WorkerPrivate::ReportError(JSContext* aCx,
                                           &stackGlobal);
 
   if (stack) {
+    JSAutoRealm ar(aCx, stackGlobal);
     report->SerializeWorkerStack(aCx, this, stack);
   }