The iOS renderer for ContentViewRoundedCorners control.

ContentViewRoundedCornersRenderer.cs

class ContentViewRoundedCornersRenderer : VisualElementRenderer<ContentView>
{
    protected override void OnElementChanged(ElementChangedEventArgs<ContentView> e)
    {
        base.OnElementChanged(e);

        if (e.OldElement != null)
        {
            return;
        }

        Layer.CornerRadius = ((ContentViewRoundedCorners) Element).CornerRadius;
    }
}