ObjC: Add support for injectable native audio and video codecs

The native interface is added in the private file
webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCPeerConnectionFactory+Native.h.

BUG=webrtc:8093

Review-Url: https://codereview.webrtc.org/3012443002
Cr-Original-Commit-Position: refs/heads/master@{#19576}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: b8853ca8d351864a2396e0bdf677f61ad166a4b6
4 files changed