Some Android devices are very finicky about how quicky output buffers
are returned back to the decoder, especially when they are associated
with a Surface.

This commit adds a new counter that keeps track of exactly how many hw
output buffers are being retained by the user, along with DEBUG level
logging that makes it easy to track the lifecycle of these buffers.
Signed-off-by: Aman Gupta <aman@tmm1.net>
Signed-off-by: Matthieu Bouron <matthieu.bouron@gmail.com>