Directly use the libyuv API for YUV conversion to I420 Bug: None Change-Id: Iea6e8fa8f7179c800ea850305170002398cb00dc Reviewed-on: https://webrtc-review.googlesource.com/17260 Commit-Queue: Niels Moller <nisse@webrtc.org> Reviewed-by: Åsa Persson <asapersson@webrtc.org> Reviewed-by: Alex Glaznev <glaznev@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Reviewed-by: Magnus Jedvert <magjed@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20681}