Update API for Objective-C RTCAudioTrack and RTCVideoTrack.

BUG=
R=tkchin@webrtc.org

Review URL: https://codereview.webrtc.org/1553743003 .

Patch from Jon Hjelle <hjon@andyet.net>.

Cr-Original-Commit-Position: refs/heads/master@{#11350}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: ca91e38a3a4e43dbf0e1f21af005e8540904f829
10 files changed