Bug 1428447 Set a loading principal on ServiceWorker WorkerPrivate objects. r=asuth

dom/workers/ServiceWorkerPrivate.cpp

@@ -1883,6 +1883,7 @@ ServiceWorkerPrivate::SpawnWorkerIfNeeded(WakeUpReason aWhy,
   if (NS_WARN_IF(!info.mPrincipal)) {
     return NS_ERROR_FAILURE;
   }
+  info.mLoadingPrincipal = info.mPrincipal;
 
   nsContentUtils::StorageAccess access =
     nsContentUtils::StorageAllowedForPrincipal(info.mPrincipal);

dom/workers/WorkerPrivate.cpp

@@ -5040,8 +5040,7 @@ WorkerPrivate::OverrideLoadInfoLoadGroup(WorkerLoadInfo& aLoadInfo,
                                          nsIPrincipal* aPrincipal)
 {
   MOZ_ASSERT(!aLoadInfo.mInterfaceRequestor);
-  MOZ_ASSERT(aLoadInfo.mPrincipal == aPrincipal /* service workers */ ||
-             aLoadInfo.mLoadingPrincipal == aPrincipal /* any other worker type */);
+  MOZ_ASSERT(aLoadInfo.mLoadingPrincipal == aPrincipal);
 
   aLoadInfo.mInterfaceRequestor =
     new WorkerLoadInfo::InterfaceRequestor(aPrincipal, aLoadInfo.mLoadGroup);