This CL prepares parts the analog AGC code to make it properly multichannel. Bug: webrtc:10859 Change-Id: I693d0d004dd2c7495ebdc60a43e9a53a441a93e0 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158896 Commit-Queue: Per Åhgren <peah@webrtc.org> Reviewed-by: Sam Zackrisson <saza@webrtc.org> Reviewed-by: Alessio Bazzica <alessiob@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29718}