The frame transformer is passed from RTPSenderInterface through the library to be eventually set in ChannelSend, where the frame transformation will occur in the follow-up CL. Insertable Streams Web API explainer: https://github.com/alvestrand/webrtc-media-streams/blob/master/explainer.md Design doc for WebRTC library changes: http://doc/1eiLkjNUkRy2FssCPLUp6eH08BZuXXoHfbbBP1ZN7EVk Bug: webrtc:11380 Change-Id: I01b2adc3c96b948d182d5401a9a4fe14cf5960a2 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171870 Commit-Queue: Tommi <tommi@webrtc.org> Reviewed-by: Per Åhgren <peah@webrtc.org> Reviewed-by: Tommi <tommi@webrtc.org> Reviewed-by: Magnus Flodman <mflodman@webrtc.org> Cr-Commit-Position: refs/heads/master@{#30946}