LibWeb: Make the Window object "inherit" from EventTarget :^)

Since Web::Bindings::WindowObject inherits from JS::GlobalObject, it
cannot also inherit from Web::Bindings::EventTargetWrapper.

However, that's not actually necessary. Instead, we simply set the
Window object's prototype to the EventTargetPrototype, and add a little
extra branch in the impl_from() function that turns the JS "this" value
into a DOM::EventTarget*.

With this, you can now call window.addEventListener()! Very cool :^)

Fixes #4758.

Userland/Libraries/LibWeb/DOM/EventTarget.h

@@ -51,7 +51,7 @@ public:
     void remove_from_event_listener_list(NonnullRefPtr<EventListener>);
 
     virtual bool dispatch_event(NonnullRefPtr<Event>) = 0;
-    virtual Bindings::EventTargetWrapper* create_wrapper(JS::GlobalObject&) = 0;
+    virtual JS::Object* create_wrapper(JS::GlobalObject&) = 0;
     Bindings::ScriptExecutionContext* script_execution_context() { return m_script_execution_context; }
 
     virtual EventTarget* get_parent(const Event&) { return nullptr; }

Userland/Libraries/LibWeb/DOM/Node.cpp

@@ -213,7 +213,7 @@ bool Node::is_editable() const
     return parent() && parent()->is_editable();
 }
 
-Bindings::EventTargetWrapper* Node::create_wrapper(JS::GlobalObject& global_object)
+JS::Object* Node::create_wrapper(JS::GlobalObject& global_object)
 {
     return wrap(global_object, *this);
 }

Userland/Libraries/LibWeb/DOM/Node.h

@@ -61,7 +61,7 @@ public:
     virtual void ref_event_target() final { ref(); }
     virtual void unref_event_target() final { unref(); }
     virtual bool dispatch_event(NonnullRefPtr<Event>) final;
-    virtual Bindings::EventTargetWrapper* create_wrapper(JS::GlobalObject&) override;
+    virtual JS::Object* create_wrapper(JS::GlobalObject&) override;
 
     virtual ~Node();
 

Userland/Libraries/LibWeb/DOM/Window.cpp

@@ -169,9 +169,9 @@ bool Window::dispatch_event(NonnullRefPtr<Event> event)
     return EventDispatcher::dispatch(*this, event, true);
 }
 
-Bindings::EventTargetWrapper* Window::create_wrapper(JS::GlobalObject&)
+JS::Object* Window::create_wrapper(JS::GlobalObject& global_object)
 {
-    ASSERT_NOT_REACHED();
+    return &global_object;
 }
 
 }

Userland/Libraries/LibWeb/DOM/Window.h

@@ -50,7 +50,7 @@ public:
     virtual void ref_event_target() override { RefCounted::ref(); }
     virtual void unref_event_target() override { RefCounted::unref(); }
     virtual bool dispatch_event(NonnullRefPtr<Event>) override;
-    virtual Bindings::EventTargetWrapper* create_wrapper(JS::GlobalObject&) override;
+    virtual JS::Object* create_wrapper(JS::GlobalObject&) override;
 
     const Document& document() const { return m_document; }
     Document& document() { return m_document; }

Userland/Libraries/LibWeb/DOM/XMLHttpRequest.cpp

@@ -113,7 +113,7 @@ bool XMLHttpRequest::dispatch_event(NonnullRefPtr<DOM::Event> event)
     return DOM::EventDispatcher::dispatch(*this, move(event));
 }
 
-Bindings::EventTargetWrapper* XMLHttpRequest::create_wrapper(JS::GlobalObject& global_object)
+JS::Object* XMLHttpRequest::create_wrapper(JS::GlobalObject& global_object)
 {
     return wrap(global_object, *this);
 }

Userland/Libraries/LibWeb/DOM/XMLHttpRequest.h

@@ -66,7 +66,7 @@ private:
     virtual void ref_event_target() override { ref(); }
     virtual void unref_event_target() override { unref(); }
     virtual bool dispatch_event(NonnullRefPtr<DOM::Event>) override;
-    virtual Bindings::EventTargetWrapper* create_wrapper(JS::GlobalObject&) override;
+    virtual JS::Object* create_wrapper(JS::GlobalObject&) override;
 
     void set_ready_state(ReadyState);