Ensure that animated key button drawable has callbacks

- The animated drawable never has callbacks set, so if nothing
  else invalidates while the AVD is drawing, we may not end
  up invalidating.  Haven't actually been able to repro the
  original issue but, this is a potential cause.

Bug: 158680912
Test: Haven't been able to repro the original issue, but
      we ensure that the rotation button still works

ehange-Id: Iba00785cf85df2e85a19e1b44a17953877514b68
Change-Id: I4dc673824e1cf068ee0eb9953c7e3264c22fa7f5