Drawing thumbnail background color for empty space in view.

- When showing landscape thumbnails in portrait, the thumbnails are
  aspect scaled to fit the width of the view, this change will draw
  a solid color to fill the other part so that we don't see the
  current edge-clamp texture effect.

Change-Id: Icf08239942f9179c66ba0f8d8ddd00f7d2a09d3c