LibWeb: Handle scenario when Window property setter is called on global

This commit fixes a regression introduced in
1528e9109c.

Turns out that the type of `this_value` in the property setter of the
Window object depends on how the variable is accessed. If the property
is accessed as a global variable, then this_value is of type `Window`.
For example:
```js
performance = null
```

However, when it is accessed as a property of the window object,
`this_value` is of type `WindowProxy`. For example:
```js
window.performance = null
```

This commit updates the window property setters generator to handle
both scenarios.

With this change https://discord.com/login works again.

Meta/Lagom/Tools/CodeGenerators/LibWeb/BindingsGenerator/IDLGenerators.cpp

@@ -3187,16 +3187,27 @@ JS_DEFINE_NATIVE_FUNCTION(@class_name@::@attribute.setter_callback@)
 }
 )~~~");
         } else if (attribute.extended_attributes.contains("Replaceable"sv)) {
-            if (interface.name.is_one_of("Window")) {
+            if (interface.name == "Window"sv) {
                 attribute_generator.append(R"~~~(
 JS_DEFINE_NATIVE_FUNCTION(@class_name@::@attribute.setter_callback@)
 {
     auto this_value = vm.this_value();
-    if (!this_value.is_object() || !is<WindowProxy>(this_value.as_object()))
-        return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "@namespaced_name@");
-    auto& window_proxy = static_cast<WindowProxy&>(this_value.as_object());
-    TRY(window_proxy.window()->internal_define_own_property("@attribute.name@", JS::PropertyDescriptor { .value = vm.argument(0), .writable = true }));
-    return JS::js_undefined();
+    JS::GCPtr<Window> window;
+    if (this_value.is_object()) {
+        if (is<WindowProxy>(this_value.as_object())) {
+            auto& window_proxy = static_cast<WindowProxy&>(this_value.as_object());
+            window = window_proxy.window();
+        } else if (is<Window>(this_value.as_object())) {
+            window = &static_cast<Window&>(this_value.as_object());
+        }
+    }
+
+    if (window) {
+        TRY(window->internal_define_own_property("@attribute.name@", JS::PropertyDescriptor { .value = vm.argument(0), .writable = true }));
+        return JS::js_undefined();
+    }
+
+    return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "@namespaced_name@");
 }
 )~~~");
             } else {

Tests/LibWeb/Text/expected/global-performance-property.txt

@@ -0,0 +1 @@
+PASS

Tests/LibWeb/Text/input/global-performance-property.html

@@ -0,0 +1,9 @@
+<script src="include.js"></script>
+<script>
+    test(() => {
+        // Test passes if this script does not throw an exception.
+        performance;
+        performance = null;
+        println("PASS");
+    });
+</script>