Update API for Objective-C RTCMediaStream.

BUG=
R=tkchin@webrtc.org

Review URL: https://codereview.webrtc.org/1558733002 .

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

Cr-Original-Commit-Position: refs/heads/master@{#11351}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 2bf9a5f11b60025a588fa58d883a191577d0e350
5 files changed