Add information about microphone gain changes to AEC3

Changes in the microphone gain are effecting the AEC in the sense
that each change in the microphone gain is a change in the echo
path seen by the AEC. This CL utilizes the ability of AEC3 to
leverage information about known changes in the analog microphone
gain.

BUG=webrtc:6018

Review-Url: https://codereview.webrtc.org/2808073002
Cr-Original-Commit-Position: refs/heads/master@{#17625}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6799553a2cbe2470115a7db01ed14f4a4c593d88
2 files changed