This CL adds the ability to set a default echo path delay to use in AEC3 when there is prior knowledge about the delay in the echo path. Bug: webrtc:8358 Change-Id: Ie368f9a6dec9f412e09bf0e095f89d84305045f9 Reviewed-on: https://webrtc-review.googlesource.com/7604 Commit-Queue: Per Åhgren <peah@webrtc.org> Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20204}