Remove I420VideoFrame::SwapFrame

The few remaining uses of this function are replaced with I420VideoFrame assignment, similar to scoped_refptr assignment.

BUG=1128
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/42889004

Cr-Original-Commit-Position: refs/heads/master@{#8844}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: deafa7b3c9a247106ad190a14c823b053eb13cf5
6 files changed