Make toVideoFrame in I420Frame return the original frame.

Bug: webrtc:7749
Change-Id: Ib9a2812e0b3b9b7c9f77ceb284f46c6cf2122467
Reviewed-on: https://webrtc-review.googlesource.com/1187
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Original-Commit-Position: refs/heads/master@{#19832}
Cr-Mirrored-From: https://webrtc.googlesource.com/src
Cr-Mirrored-Commit: 7d1f493a8b042b9ccf6993bb078c83bb0d992094
1 file changed