How to use XamlWriter and XamlReader

gistfile1.cs

class Program
{
    static void Main(string[] args)
    {

        var test = new Test {Name = "Rune", Number = 35};

        var serialized = XamlWriter.Save(test);

        var deserialized = (Test) XamlReader.Parse(serialized);

    }
}

public class Test
{
    public string Name { get; set; }
    public int Number { get; set; }
}

XamlWriter.Save() and XamlReader.Parse() doesn't exist for me? which assembly did you get it from?