[WPF]GridのRowDefinitionのHeightをWindowのHeightに応じて任意に変化させる的な

DoubleToGridLengthConverter.cs

using System;
using System.Windows;
using System.Windows.Data;

namespace WpfApplication1
{
    public class DoubleToGridLengthConverter : IValueConverter
    {
        private static readonly GridLengthConverter Conv = new GridLengthConverter();

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return Conv.ConvertFrom((double)value < 200 ? "Auto" : "*");
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

MainWindow.xaml

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfApplication1="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <wpfApplication1:DoubleToGridLengthConverter x:Key="DoubleToGridLengthConverter"/>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="{Binding RelativeSource={RelativeSource AncestorType=Window}, Path=Height, Converter={StaticResource DoubleToGridLengthConverter}}"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Border Grid.Row="0" Background="IndianRed" Height="20"/>
        <Border Grid.Row="1" Background="CornflowerBlue"/>
    </Grid>
</Window>