6030a129c0
We want this because otherwise the ACM uses its mutex to protect an encoder that's owned by someone else. That someone else may easily slip up and delete or otherwise touch the encoder before making sure that the ACM has stopped using it, bypassing the lock. BUG=webrtc:5028 Review URL: https://codereview.webrtc.org/1702943002 Cr-Commit-Position: refs/heads/master@{#11909}