VoE2 API draft

BUG=4690
R=jmarusic@webrtc.org, kwiberg@webrtc.org, mflodman@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/50029004

Cr-Commit-Position: refs/heads/master@{#9392}
8 files changed