LibWeb: Use ResizeObserver instance as this in callback function

Author: https://github.com/kalenikaliaksandr
Commit: 1cc9fb6135
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6117
Reviewed-by: https://github.com/tcl3

Libraries/LibWeb/ResizeObserver/ResizeObserver.cpp

@@ -116,7 +116,7 @@ void ResizeObserver::invoke_callback(ReadonlySpan<GC::Ref<ResizeObserverEntry>>
         MUST(wrapped_records->create_data_property(property_index, record.ptr()));
     }
 
-    (void)WebIDL::invoke_callback(callback, JS::js_undefined(), WebIDL::ExceptionBehavior::Report, { { wrapped_records } });
+    (void)WebIDL::invoke_callback(callback, this, WebIDL::ExceptionBehavior::Report, { { wrapped_records } });
 }
 
 void ResizeObserver::unregister_observer_if_needed()

Tests/LibWeb/Text/input/ResizeObserver/observe.html

@@ -23,7 +23,11 @@
             });
         }
 
-        const resizeObserver = new ResizeObserver(entries => {
+        const resizeObserver = new ResizeObserver(function (entries) {
+            if (this !== resizeObserver) {
+                println("this is not the ResizeObserver instance inside callback");
+            }
+
             for (let entry of entries) {
                 const { width, height } = entry.contentRect;
                 println(`Size changed: ${width}px x ${height}px`);