LibWeb: Implement window.stop()

Fixes a handful of timeouts on WPT.

Libraries/LibWeb/HTML/Navigable.cpp

@@ -2234,4 +2234,18 @@ void Navigable::unregister_navigation_observer(Badge<NavigationObserver>, Naviga
     VERIFY(was_removed);
 }
 
+// https://html.spec.whatwg.org/multipage/document-lifecycle.html#nav-stop
+void Navigable::stop_loading()
+{
+    // 1. Let document be navigable's active document.
+    auto document = active_document();
+
+    // 2. If document's unload counter is 0, and navigable's ongoing navigation is a navigation ID, then set the ongoing navigation for navigable to null.
+    if (document->unload_counter() == 0 && ongoing_navigation().has<String>())
+        set_ongoing_navigation(Empty {});
+
+    // 3. Abort a document and its descendants given document.
+    document->abort_a_document_and_its_descendants();
+}
+
 }