Some changes need access to both the APM interface and the AECs,
hence we can't make the changes inside the AECs themselves.
The proxies also make it easy to drop support for individual parts of the
interfaces one at a time.
Bug: webrtc:9535
Change-Id: I3398e1182157f7d8b1e4c455060b830b61c20dd9
Reviewed-on: https://webrtc-review.googlesource.com/94500
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24317}
