How do I use a NavigationPageRenderer in my Xamarin application to customize the top navigation bar?

Question

I hoped I could use the Shell.TitleView to define the top navigation bar of my Xamarin application’s pages (the one with the hamburger icon, the back button, etc). Unfortunately, it doesn’t let you center the text perfectly, as you can read here and here.

I already made other custom renderers, but I’m experiencing difficulties implementing the NavigationPageRenderer. This is the code I copied from the Web:

[assembly: ExportRenderer(typeof(CustomNavigation), typeof(CustomNavigationRenderer))]
namespace MyNamespace {
    internal class CustomNavigationRenderer : NavigationPageRenderer {
        public CustomNavigationRenderer(Context context) : base(context) { }

        protected override void OnLayout(bool changed, int l, int t, int r, int b) {
            base.OnLayout(changed, l, t, r, b);
            var toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);

            if (toolbar == null) return;

            for (var i = 0; i < toolbar.ChildCount; i++) {
                var x = toolbar.GetChildAt(i);
            }
        }
    }
}

I don’t know what this code does, and I tried to put a breakpoint at the beginning of the OnLayout() method to understand the effect of the method itself. However, the breakpoint is never reached. For my other custom renderers, I usually created a class like MyCustomEntry.cs inside the shared project of the Xamarin application, and I referenced it in my XAML files like that:

<controls:CustomEntry Placeholder="..."/>

I checked that controls reference the correct location on my project, and it does. I thought the NavigationPageRenderer should be used like that, but unfortunately, I was wrong, since Visual Studio tells me this:

Inside the shared Xamarin project, I created an empty class CustomNavigation:

public class CustomNavigation : NavigationPage { }

How do I use the CustomNavigationRenderer?