LibWeb: Implement `Navigator.serviceWorker`

This currently returns a stubbed `ServiceWorkerContainer` object.

Userland/Libraries/LibWeb/HTML/Navigator.cpp

@@ -12,6 +12,7 @@
 #include <LibWeb/Clipboard/Clipboard.h>
 #include <LibWeb/HTML/Navigator.h>
 #include <LibWeb/HTML/Scripting/Environments.h>
+#include <LibWeb/HTML/ServiceWorkerContainer.h>
 #include <LibWeb/HTML/Window.h>
 #include <LibWeb/Loader/ResourceLoader.h>
 #include <LibWeb/Page/Page.h>
@@ -64,6 +65,7 @@ void Navigator::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_plugin_array);
     visitor.visit(m_clipboard);
     visitor.visit(m_user_activation);
+    visitor.visit(m_service_worker_container);
 }
 
 JS::NonnullGCPtr<MimeTypeArray> Navigator::mime_types()
@@ -113,4 +115,11 @@ Optional<FlyString> Navigator::do_not_track() const
     return {};
 }
 
+JS::NonnullGCPtr<ServiceWorkerContainer> Navigator::service_worker()
+{
+    if (!m_service_worker_container)
+        m_service_worker_container = heap().allocate<ServiceWorkerContainer>(realm(), realm());
+    return *m_service_worker_container;
+}
+
 }

Userland/Libraries/LibWeb/HTML/Navigator.h

@@ -54,6 +54,8 @@ public:
 
     Optional<FlyString> do_not_track() const;
 
+    JS::NonnullGCPtr<ServiceWorkerContainer> service_worker();
+
     static WebIDL::Long max_touch_points();
 
     virtual ~Navigator() override;
@@ -77,6 +79,9 @@ private:
 
     // https://html.spec.whatwg.org/multipage/interaction.html#dom-navigator-useractivation
     JS::GCPtr<UserActivation> m_user_activation;
+
+    // https://w3c.github.io/ServiceWorker/#navigator-serviceworker
+    JS::GCPtr<ServiceWorkerContainer> m_service_worker_container;
 };
 
 }

Userland/Libraries/LibWeb/HTML/Navigator.idl

@@ -6,6 +6,7 @@
 #import <HTML/NavigatorOnLine.idl>
 #import <HTML/NavigatorConcurrentHardware.idl>
 #import <HTML/PluginArray.idl>
+#import <HTML/ServiceWorkerContainer.idl>
 #import <HTML/UserActivation.idl>
 #import <StorageAPI/NavigatorStorage.idl>
 
@@ -25,6 +26,9 @@ interface Navigator {
 
     // https://www.w3.org/TR/tracking-dnt/#dom-navigator-donottrack
     readonly attribute DOMString? doNotTrack;
+
+    // https://w3c.github.io/ServiceWorker/#navigator-serviceworker
+    [SecureContext, SameObject] readonly attribute ServiceWorkerContainer serviceWorker;
 };
 
 // NOTE: As NavigatorContentUtils, NavigatorCookies, NavigatorPlugins, and NavigatorAutomationInformation