When producing an invisible ARF, the time stamp counters aren't
updated since the last time stamp is seen by the codec twice. The
prior code was trapping this case with refresh_alt_ref, but this isn't
correct for other uses of the ARF. Instead, use the show_frame flag.
Change-Id: If67fff7c6c66a3606698e34e2fb5731f56b4a223
21173e1999