> Using a separate view for drawing the popup. This allows us to use elevation
property instead of drawing the shadow as bitmap.
> During the thumb animation, invalidating the full track width, instead of
invalidating the track and thumb separately.
> The thumb path is calculated at 0,0 and drawn using canvas.translate().
This avoids recalculating the path on every scroll.
Change-Id: I48741e5b4432df0d939016db284d7aaf52cc2aa6
5d9fb0e92f