LibWeb: Make PolicyContainer GC allocated

This is required to store Content Security Policies, as their
Directives are implemented as subclasses with overridden virtual
functions. Thus, they cannot be stored as generic Directive classes, as
it'll lose the ability to call overridden functions when they are
copied.

Libraries/LibWeb/HTML/SerializedPolicyContainer.cpp

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2025, Luke Wilde <luke@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
+#include <LibWeb/HTML/SerializedPolicyContainer.h>
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder& encoder, Web::HTML::SerializedPolicyContainer const& serialized_policy_container)
+{
+    TRY(encoder.encode(serialized_policy_container.embedder_policy));
+    TRY(encoder.encode(serialized_policy_container.referrer_policy));
+
+    return {};
+}
+
+template<>
+ErrorOr<Web::HTML::SerializedPolicyContainer> decode(Decoder& decoder)
+{
+    Web::HTML::SerializedPolicyContainer serialized_policy_container {};
+
+    serialized_policy_container.embedder_policy = TRY(decoder.decode<Web::HTML::EmbedderPolicy>());
+    serialized_policy_container.referrer_policy = TRY(decoder.decode<Web::ReferrerPolicy::ReferrerPolicy>());
+
+    return serialized_policy_container;
+}
+
+}