The factory for EchoControl is changed from an rtc::Callback1 to an
interface. This avoids using rtc::Callback1 outside of WebRTC.
This also makes the EchoControl factory more similar to other
factories in the code base.
Bug: webrtc:8345
Change-Id: Ie61b9416ed771f8c756326736d17e339eb768469
Reviewed-on: https://webrtc-review.googlesource.com/8900
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20272}
002ef28272