LibWeb+LibJS: Let JS::Realm::HostDefined objects mark things during GC

This allows us to mark the HTML::Window from our window environment
settings object.

Userland/Libraries/LibJS/Runtime/Realm.cpp

@@ -115,9 +115,12 @@ void Realm::set_global_object(Object* global_object, Object* this_value)
 
 void Realm::visit_edges(Visitor& visitor)
 {
+    Base::visit_edges(visitor);
     visitor.visit(m_intrinsics);
     visitor.visit(m_global_object);
     visitor.visit(m_global_environment);
+    if (m_host_defined)
+        m_host_defined->visit_edges(visitor);
 }
 
 }

Userland/Libraries/LibJS/Runtime/Realm.h

@@ -25,6 +25,8 @@ class Realm final
 public:
     struct HostDefined {
         virtual ~HostDefined() = default;
+
+        virtual void visit_edges(Cell::Visitor&) { }
     };
 
     static Realm* create(VM&);

Userland/Libraries/LibWeb/HTML/Scripting/WindowEnvironmentSettingsObject.cpp

@@ -16,6 +16,14 @@ WindowEnvironmentSettingsObject::WindowEnvironmentSettingsObject(Window& window,
 {
 }
 
+WindowEnvironmentSettingsObject::~WindowEnvironmentSettingsObject() = default;
+
+void WindowEnvironmentSettingsObject::visit_edges(JS::Cell::Visitor& visitor)
+{
+    EnvironmentSettingsObject::visit_edges(visitor);
+    visitor.visit(m_window.ptr());
+}
+
 // https://html.spec.whatwg.org/multipage/window-object.html#set-up-a-window-environment-settings-object
 void WindowEnvironmentSettingsObject::setup(AK::URL const& creation_url, NonnullOwnPtr<JS::ExecutionContext> execution_context, Optional<Environment> reserved_environment, AK::URL top_level_creation_url, Origin top_level_origin)
 {

Userland/Libraries/LibWeb/HTML/Scripting/WindowEnvironmentSettingsObject.h

@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <LibJS/Heap/Cell.h>
 #include <LibWeb/HTML/Scripting/Environments.h>
-#include <LibWeb/HTML/Window.h>
 
 namespace Web::HTML {
 
@@ -15,7 +15,7 @@ class WindowEnvironmentSettingsObject final : public EnvironmentSettingsObject {
 public:
     static void setup(AK::URL const& creation_url, NonnullOwnPtr<JS::ExecutionContext>, Optional<Environment>, AK::URL top_level_creation_url, Origin top_level_origin);
 
-    virtual ~WindowEnvironmentSettingsObject() override = default;
+    virtual ~WindowEnvironmentSettingsObject() override;
 
     virtual JS::GCPtr<DOM::Document> responsible_document() override;
     virtual String api_url_character_encoding() override;
@@ -26,7 +26,9 @@ public:
 private:
     WindowEnvironmentSettingsObject(Window&, NonnullOwnPtr<JS::ExecutionContext>);
 
-    WeakPtr<Window> m_window;
+    virtual void visit_edges(JS::Cell::Visitor&) override;
+
+    JS::GCPtr<Window> m_window;
 };
 
 }