LibWeb: Implement WindowEventHandlers

Author: https://github.com/Lubrsi
Commit: 3fe66bddf4
Pull-request: https://github.com/SerenityOS/serenity/pull/14406
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.h

@@ -7,20 +7,28 @@
 #pragma once
 
 #include <LibWeb/HTML/HTMLElement.h>
+#include <LibWeb/HTML/WindowEventHandlers.h>
 
 namespace Web::HTML {
 
 // NOTE: This element is marked as obsolete, but is still listed as required by the specification.
-class HTMLFrameSetElement final : public HTMLElement {
+class HTMLFrameSetElement final
+    : public HTMLElement
+    , public WindowEventHandlers {
 public:
     using WrapperType = Bindings::HTMLFrameSetElementWrapper;
 
     HTMLFrameSetElement(DOM::Document&, DOM::QualifiedName);
     virtual ~HTMLFrameSetElement() override;
 
+    virtual void parse_attribute(FlyString const&, String const&) override;
+
 private:
     // ^HTML::GlobalEventHandlers
     virtual EventTarget& global_event_handlers_to_event_target(FlyString const& event_name) override;
+
+    // ^HTML::WindowEventHandlers
+    virtual EventTarget& window_event_handlers_to_event_target() override;
 };
 
 }