I believe it is custom made and it shouldn't be complicated to make one yourself. It consists of a panel that is higher than the screen and has a draggable upper part. You can track Manipulation* events on it and when user starts dragging upwards, you can use RenderTransforms
to move the entire control up and down.
For smoother effect use animations to slide the upper/lower part into its place. You can easily construct such animations in code and apply them on the fly.