MainForm.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace AsyncBrowserExample
{
	public partial class MainForm : Form
	{
		public MainForm()
		{
			InitializeComponent();

			SetLoadingCircleStatus(true, true);
		}

		protected override async void OnLoad(EventArgs e)
		{
			base.OnLoad(e);

			await LoadDocumentAsync(new Uri("https://msdn.microsoft.com/ru-ru/"));
		}

		private async Task LoadDocumentAsync(Uri targetUri)
		{
			try
			{
				IAsyncResult result = BeginInvoke(new Action<Uri>(DoNavigate), targetUri);

				await Task.Factory.FromAsync(result, EndInvoke);
			}
			catch (Exception exc)
			{
				MessageBox.Show(exc.Message, "Exception occured.");
			}
			finally { }
		}

		private void DoNavigate(Uri targetUri)
		{
			Browser.Navigate(targetUri);
		}

		private void SetLoadingCircleStatus(bool visible, bool active)
		{
			LoadingCircle.Visible = visible;
			LoadingCircle.Active = active;
		}

		private void HandleDocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
		{
			SetLoadingCircleStatus(false, false);

			var browser = sender as WebBrowser;
			if (browser != null)
			{
				browser.Visible = true;
			}
		}
	}
}