It requires a new NetEq method, but it can no longer fail. And we no longer need to use AcmReceiver::decoders_, which we're trying to eliminate. (This is a re-land of https://codereview.webrtc.org/2342313002.) BUG=webrtc:5801 Review-Url: https://codereview.webrtc.org/2348233002 Cr-Commit-Position: refs/heads/master@{#14304}