Run URL check using a task

Tasks/UrlTester/MainWindow.xaml.cs

@@ -25,11 +25,22 @@ public partial class MainWindow : Window
 
     public void GetUrl(object sender, RoutedEventArgs e)
     {
+        var tester = new DT2.UrlTester();
         var stopWatch = new Stopwatch();
+
+        tester.PageStart += (_) =>
+        {
             stopWatch.Start();
-        int size = new DT2.UrlTester().GetUrlSync(urlBox.Text);
+        };
+
+        tester.PageLoaded += (_, size) =>
+        {
             stopWatch.Stop();
             bytesBox.Text = $"{size} bytes";
             timeBox.Text = $"{stopWatch.ElapsedMilliseconds} ms";
+            timeBar.Value = stopWatch.ElapsedMilliseconds;
+        };
+
+        _ = tester.GetUrlAsync(urlBox.Text);
     }
 }