This CL contains various cleanups/corrections to the multichannel AEC code. The changes have been shown to be bitexact over a large dataset. Bug: webrtc:10913 Change-Id: Idd3e410b04527666e052f57ad81d0ac9eef3179b Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157173 Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org> Commit-Queue: Per Åhgren <peah@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29530}