LibWeb: Treat global as EventTarget in notify_about_rejected_promises

We only need to know that the Global Object of the environment is an
event target in order to dispatch an event on it. This resolves a FIXME
where we assumed that the only type of Global in LibWeb is HTML::Window.

Userland/Libraries/LibWeb/HTML/Scripting/Environments.cpp

@@ -234,12 +234,15 @@ void EnvironmentSettingsObject::notify_about_rejected_promises(Badge<EventLoop>)
     m_about_to_be_notified_rejected_promises_list.clear();
 
     // 4. Let global be settings object's global object.
-    auto& global = global_object();
+    // We need this as an event target for the unhandledrejection event below
+    auto& global = verify_cast<DOM::EventTarget>(global_object());
 
     // 5. Queue a global task on the DOM manipulation task source given global to run the following substep:
     queue_global_task(Task::Source::DOMManipulation, global, [this, &global, list = move(list)] {
+        auto& realm = global.realm();
+
         // 1. For each promise p in list:
-        for (auto promise : list) {
+        for (auto const& promise : list) {
 
             // 1. If p's [[PromiseIsHandled]] internal slot is true, continue to the next iteration of the loop.
             if (promise->is_handled())
@@ -257,12 +260,10 @@ void EnvironmentSettingsObject::notify_about_rejected_promises(Badge<EventLoop>)
                 /* .promise = */ JS::make_handle(*promise),
                 /* .reason = */ promise->result(),
             };
-            // FIXME: This currently assumes that global is a WindowObject.
-            auto& window = verify_cast<HTML::Window>(global);
 
-            auto promise_rejection_event = PromiseRejectionEvent::create(window.realm(), HTML::EventNames::unhandledrejection, event_init);
+            auto promise_rejection_event = PromiseRejectionEvent::create(realm, HTML::EventNames::unhandledrejection, event_init);
 
-            bool not_handled = window.dispatch_event(*promise_rejection_event);
+            bool not_handled = global.dispatch_event(*promise_rejection_event);
 
             // 3. If notHandled is false, then the promise rejection is handled. Otherwise, the promise rejection is not handled.
 
@@ -273,7 +274,7 @@ void EnvironmentSettingsObject::notify_about_rejected_promises(Badge<EventLoop>)
             // This algorithm results in promise rejections being marked as handled or not handled. These concepts parallel handled and not handled script errors.
             // If a rejection is still not handled after this, then the rejection may be reported to a developer console.
             if (not_handled)
-                HTML::report_exception_to_console(promise->result(), realm(), ErrorInPromise::Yes);
+                HTML::report_exception_to_console(promise->result(), realm, ErrorInPromise::Yes);
         }
     });
 }