AppDelegate.cs

using Foundation;
using UIKit;

namespace DebuggerIssue {
    [Register("AppDelegate")]
    public class AppDelegate : UIApplicationDelegate
    {
        public override UIWindow Window
        {
            get;
            set;
        }

        public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions)
        {
            UIDevice.CurrentDevice.BeginInvokeOnMainThread (async () => {
                var client = new System.Net.Http.HttpClient ();
                var result = await client.GetStringAsync ("http://xamarin.com");
            });

            return true;
        }
    }
}