title: How to change font size of navigationPage in Xamarin?
body: <p>I have a Xamarin.Form project.
  I want to change the font size of navigationBar in Win phone 8.1.
  Here is my code.</p>
  
  <pre><code>public partial class App: Application
  {
    public App()
    {
      InitializeComponent();
      MainPage = new NavigationPage(new LoginPage))
      {
        BarBackgroundColor = Color.Red,
        //BarFontSize = "Large"???
      };
    }
  }
  </code></pre>
  
  <p>How can I change fontsize of navigation bar?</p>