This CL adds a temporary flag for specifying that the legacy AEC2 should
be used.
Bug: webrtc:10366
Change-Id: Ie3edaa1560cdc1282b62242beb67aa6fee7f2841
Reviewed-on: https://webrtc-review.googlesource.com/c/124980
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26891}