Add support for 3-byte headers in VideoToolbox NALU parser.

BUG=webrtc:6278
R=tkchin@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/2356793002 .

Cr-Original-Commit-Position: refs/heads/master@{#14889}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cb18ee61270694e743970100bf2871bd67a44906
4 files changed