These interfaces will be used by the future refactoring that will allow clients to provide custom codec implementations. Change-Id: If199bc2807e1c27094c05983c62fa43d2eec5700 Bug: webrtc:7760 Reviewed-on: https://chromium-review.googlesource.com/522065 Commit-Queue: Sami Kalliomäki <sakal@webrtc.org> Reviewed-by: Magnus Jedvert <magjed@webrtc.org> Reviewed-by: Bjorn Mellem <mellem@webrtc.org> Cr-Commit-Position: refs/heads/master@{#18441}