This new VideoFrame class closesly matches the C++ webrtc::VideoFrame and webrtc::VideoFrameBuffer classes. It's supposed to replace the existing VideoRenderer.I420Frame. The purpose is to clean up the code and support more frame formats. BUG=webrtc:7749 Review-Url: https://codereview.webrtc.org/2915083002 Cr-Commit-Position: refs/heads/master@{#18404}