LibWeb: Reorganize window.parent so it looks a bit more like the spec

Userland/Libraries/LibWeb/Bindings/WindowObject.cpp

@@ -396,22 +396,13 @@ JS_DEFINE_NATIVE_FUNCTION(WindowObject::top_getter)
     return top_window.wrapper();
 }
 
-// https://html.spec.whatwg.org/multipage/browsers.html#dom-parent
 JS_DEFINE_NATIVE_FUNCTION(WindowObject::parent_getter)
 {
     auto* impl = TRY(impl_from(vm, global_object));
-
-    auto* this_browsing_context = impl->associated_document().browsing_context();
-    if (!this_browsing_context)
+    auto* parent = impl->parent();
+    if (!parent)
         return JS::js_null();
-
-    if (this_browsing_context->parent()) {
-        VERIFY(this_browsing_context->parent()->active_document());
-        auto& parent_window = this_browsing_context->parent()->active_document()->window();
-        return parent_window.wrapper();
-    }
-    VERIFY(this_browsing_context == &this_browsing_context->top_level_browsing_context());
-    return impl->wrapper();
+    return parent->wrapper();
 }
 
 JS_DEFINE_NATIVE_FUNCTION(WindowObject::document_getter)

Userland/Libraries/LibWeb/DOM/Window.cpp

@@ -451,4 +451,29 @@ RefPtr<HTML::Storage> Window::local_storage()
     });
 }
 
+// https://html.spec.whatwg.org/multipage/browsers.html#dom-parent
+Window* Window::parent()
+{
+    // 1. Let current be this Window object's browsing context.
+    auto* current = associated_document().browsing_context();
+
+    // 2. If current is null, then return null.
+    if (!current)
+        return nullptr;
+
+    // 3. If current is a child browsing context of another browsing context parent,
+    //    then return parent's WindowProxy object.
+    if (current->parent()) {
+        VERIFY(current->parent()->active_document());
+        return &current->parent()->active_document()->window();
+    }
+
+    // 4. Assert: current is a top-level browsing context.
+    VERIFY(current->is_top_level());
+
+    // FIXME: 5. Return current's WindowProxy object.
+    VERIFY(current->active_document());
+    return &current->active_document()->window();
+}
+
 }

Userland/Libraries/LibWeb/DOM/Window.h

@@ -100,6 +100,8 @@ public:
 
     RefPtr<HTML::Storage> local_storage();
 
+    Window* parent();
+
 private:
     explicit Window(Document&);