Replace AdaptCount with a single counter.

There is still a counter for the active counts for the
scaling, but these will be removed at a later date.

BUG=webrtc:11392

Change-Id: Ie9bcf3f744a0bbac601f0da61197f4bac1e9f879
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169447
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@google.com>
Cr-Commit-Position: refs/heads/master@{#30701}