SupportLeanbackShowcase: bring gradle, build tools, lib up to date am: 15f5a3351f
am: 302ab270d6

* commit '302ab270d64c73a701e87131474d00c2aedaee8a':
  SupportLeanbackShowcase: bring gradle, build tools, lib up to date

Change-Id: I36b230cd2292aa13ae7dcedfc62815bf9bed2ad3