LibWeb: Implement fire a download request navigate event

Author: https://github.com/ADKaster
Commit: https://github.com/SerenityOS/serenity/commit/0f8ae12d44
Pull-request: https://github.com/SerenityOS/serenity/pull/21199

Userland/Libraries/LibWeb/HTML/Navigation.cpp

@@ -1294,4 +1294,35 @@ bool Navigation::fire_a_push_replace_reload_navigate_event(
     return inner_navigate_event_firing_algorithm(navigation_type, destination, user_involvement, move(form_data_entry_list), {}, move(classic_history_api_state));
 }
 
+// https://html.spec.whatwg.org/multipage/nav-history-apis.html#fire-a-download-request-navigate-event
+bool Navigation::fire_a_download_request_navigate_event(AK::URL destination_url, UserNavigationInvolvement user_involvement, String filename)
+{
+    auto& realm = relevant_realm(*this);
+    auto& vm = this->vm();
+
+    // 1. Let event be the result of creating an event given NavigateEvent, in navigation's relevant realm.
+    // 2. Set event's classic history API state to classicHistoryAPIState.
+    // AD-HOC: These are handled in the inner algorithm
+
+    // 3. Let destination be a new NavigationDestination created in navigation's relevant realm.
+    auto destination = NavigationDestination::create(realm);
+
+    // 4. Set destination's URL to destinationURL.
+    destination->set_url(destination_url);
+
+    // 5. Set destination's entry to null.
+    destination->set_entry(nullptr);
+
+    // 6. Set destination's state to StructuredSerializeForStorage(null).
+    destination->set_state(MUST(structured_serialize_for_storage(vm, JS::js_null())));
+
+    // 7. Set destination's is same document to false.
+    destination->set_is_same_document(false);
+
+    // 8. Return the result of performing the inner navigate event firing algorithm given navigation,
+    //   "push", event, destination, userInvolvement, null, and filename.
+    // AD-HOC: We don't pass the event, but we do pass the classic_history_api state at the end to be set later
+    return inner_navigate_event_firing_algorithm(Bindings::NavigationType::Push, destination, user_involvement, {}, move(filename), {});
+}
+
 }

Userland/Libraries/LibWeb/HTML/Navigation.h

@@ -118,6 +118,7 @@ public:
         Optional<Vector<XHR::FormDataEntry>&> form_data_entry_list = {},
         Optional<SerializationRecord> navigation_api_state = {},
         Optional<SerializationRecord> classic_history_api_state = {});
+    bool fire_a_download_request_navigate_event(AK::URL destination_url, UserNavigationInvolvement user_involvement, String filename);
 
     virtual ~Navigation() override;