LibWeb: Add a stub PolicyContainer struct

Userland/Libraries/LibWeb/Forward.h

@@ -270,6 +270,7 @@ class MessageEvent;
 class MessagePort;
 class Origin;
 class PageTransitionEvent;
+struct PolicyContainer;
 class PromiseRejectionEvent;
 class WorkerDebugConsoleClient;
 class Storage;

Userland/Libraries/LibWeb/HTML/PolicyContainers.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/origin.html#policy-container
+// A policy container is a struct containing policies that apply to a Document, a WorkerGlobalScope, or a WorkletGlobalScope. It has the following items:
+struct PolicyContainer {
+    // https://html.spec.whatwg.org/multipage/origin.html#policy-container-csp-list
+    // FIXME: A CSP list, which is a CSP list. It is initially empty.
+
+    // https://html.spec.whatwg.org/multipage/origin.html#policy-container-embedder-policy
+    // FIXME: An embedder policy, which is an embedder policy. It is initially a new embedder policy.
+
+    // https://html.spec.whatwg.org/multipage/origin.html#policy-container-referrer-policy
+    // FIXME: A referrer policy, which is a referrer policy. It is initially the default referrer policy.
+};
+
+}