Add video timing frames to set of default RTP header extensions

BUG=webrtc:7594

Review-Url: https://codereview.webrtc.org/2994893002
Cr-Original-Commit-Position: refs/heads/master@{#19449}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: eb13f5e40048bc4305e35bb9c18d5ce969f63f51
1 file changed