I420VideoFrame: Remove function ResetSize

This is a partial reland of https://webrtc-codereview.appspot.com/39939004/.

The original CL was reverted because ViECapturer use ResetSize/IsZeroSize on |captured_frame_| as a check to make sure each captured frame is only delivered once. Removing ResetSize introduced a race condition where a captured frame could be delivered multiple times.

I have fixed this problem in this CL by replacing ResetSize with scoped_ptr::release.

BUG=4352
R=perkj@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/39359004

Cr-Commit-Position: refs/heads/master@{#8561}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8561 4adac7df-926f-26a2-2b94-8c16560cd09d
9 files changed