webrtc::VideoFrame::set_video_frame_buffer webrtc::VideoFrame::ConvertNativeToI420Frame cricket::WebRtcVideoFrame::InitToBlack VideoFrameBuffer::data VideoFrameBuffer::stride VideoFrameBuffer::MutableData TBR=tkchin@webrtc.org # Refactoring affecting RTCVideoFrame BUG=webrtc:5682 Review-Url: https://codereview.webrtc.org/2065733003 Cr-Commit-Position: refs/heads/master@{#13183}