This is done to avoid having a nonlinear component in the AEC path. Now the linear delay and sum is run before the AEC and the postfilter after it. This change landed originally at: https://codereview.webrtc.org/1982183002/ R=peah@webrtc.org TBR=henrik.lundin@webrtc.org Review URL: https://codereview.webrtc.org/2110593003 . Cr-Commit-Position: refs/heads/master@{#13371}