LibWeb: Add Window.parent and fix Window.top attributes

This returns the parent frame of the current frame. If it's the
main frame, it returns itself.

Also fixes the attributes of Window.top, as they were accidentally
being passed in as the setter.

Required by Web Platform Tests.

Userland/Libraries/LibWeb/Bindings/WindowObject.cpp

@@ -67,7 +67,8 @@ void WindowObject::initialize_global_object()
  define_property("window", this, JS::Attribute::Enumerable);
  define_property("frames", this, JS::Attribute::Enumerable);
  define_property("self", this, JS::Attribute::Enumerable);
- define_native_property("top", top_getter, JS::Attribute::Enumerable);
+ define_native_property("top", top_getter, nullptr, JS::Attribute::Enumerable);
+ define_native_property("parent", parent_getter, nullptr, JS::Attribute::Enumerable);
  define_native_property("document", document_getter, nullptr, JS::Attribute::Enumerable);
  define_native_property("performance", performance_getter, nullptr, JS::Attribute::Enumerable);
  define_native_property("screen", screen_getter, nullptr, JS::Attribute::Enumerable);
@@ -366,6 +367,22 @@ JS_DEFINE_NATIVE_GETTER(WindowObject::top_getter)
  return top_window.wrapper();
 }
 
+JS_DEFINE_NATIVE_GETTER(WindowObject::parent_getter)
+{
+ auto* impl = impl_from(vm, global_object);
+ if (!impl)
+ return {};
+ auto* this_frame = impl->document().frame();
+ VERIFY(this_frame);
+ if (this_frame->parent()) {
+ VERIFY(this_frame->parent()->document());
+ auto& parent_window = this_frame->parent()->document()->window();
+ return parent_window.wrapper();
+ }
+ VERIFY(this_frame == &this_frame->main_frame());
+ return impl->wrapper();
+}
+
 JS_DEFINE_NATIVE_GETTER(WindowObject::document_getter)
 {
  auto* impl = impl_from(vm, global_object);

Userland/Libraries/LibWeb/Bindings/WindowObject.h

@@ -90,6 +90,8 @@ class WindowObject final
  JS_DECLARE_NATIVE_GETTER(inner_width_getter);
  JS_DECLARE_NATIVE_GETTER(inner_height_getter);
 
+ JS_DECLARE_NATIVE_GETTER(parent_getter);
+
  JS_DECLARE_NATIVE_FUNCTION(alert);
  JS_DECLARE_NATIVE_FUNCTION(confirm);
  JS_DECLARE_NATIVE_FUNCTION(prompt);