The new RTCVideoSource interface can be used by custom implementations of RTCVideoCapturer.
BUG=webrtc:7177
TBR=tommi
Review-Url: https://codereview.webrtc.org/2745193002
Cr-Commit-Position: refs/heads/master@{#17409}
Moves webrtc/common_video/rotation.h and parts of
webrtc/common_video/include/video_frame_buffer.h and
webrtc/video_frame.h, and adds to a new GN target api:video_frame_api.
BUG=webrtc:5880
Review-Url: https://codereview.webrtc.org/2517173004
Cr-Commit-Position: refs/heads/master@{#15993}