Why Xamarin not supports HttpClient?

private string GetHtmlCode(string url)
        {
            var httpClient = new HttpClient();
            var httpResponseMessage = httpClient.GetAsync(url).Result;         
            Stream res = httpResponseMessage.Content.ReadAsStreamAsync().Result;
            //Запись в поток
            StreamReader reader = new StreamReader(res, Encoding.UTF8);
            return reader.ReadToEnd();
        }

using System.Net.Http - no