This work is also done as a preparation for adding stereo support to the FineAudioBuffer. Review hints: Actual changes are in modules/audio_device/fine_audio_buffer.h,cc, the rest is just adaptations to match these changes. We do have a forked ADM today, hence, some changes are duplicated. The changes have been verified on all affected platforms. Bug: webrtc:6560 Change-Id: I413af41c43809f61455c45ad383fc4b1c65e1fa1 Reviewed-on: https://webrtc-review.googlesource.com/70781 Commit-Queue: Henrik Andreassson <henrika@webrtc.org> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22938}