Path subclass for drawing a line that fills its available space in silverlight

FillingLine.cs

public class FillingLine : Path
{
    Size lastFinalSize;

    protected override Size MeasureOverride(Size availableSize)
    {
        return new Size(0, 0);
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        // track the last size so that we don't re-calculate when we don't need to.
        // this is especially important since setting the Data triggers a new layout!
        if (lastFinalSize != finalSize)
        {
            lastFinalSize = finalSize;
            Data = CreatePathData(finalSize);
        }
        return finalSize;
    }

    static PathGeometry CreatePathData(Size size)
    {
        Rect rect;

        if (size.Height == 1)
        {
            rect = new Rect(0, 0.5, size.Width, 0);
        }
        else if (size.Width == 1)
        {
            rect = new Rect(0.5, 0, 0, size.Height);
        }
        else
        {
            rect = new Rect(0.5, 0.5, size.Width - 0.5, size.Height - 0.5);
        }

        return new PathGeometry
                {
                    Figures =
                        {
                            new PathFigure
                            {
                                StartPoint = new Point(rect.Left, rect.Top),
                                Segments =
                                    {
                                        new LineSegment {Point = new Point(rect.Right, rect.Bottom)}
                                    }
                            }
                        }
                };
    }
}