zhihuang 633f6fe004 Add the OnAddTrack callback for Objective-C wrapper.
Created an Obj-C wrapper for the callback OnAddTrack in this CL since it has been added to native C++ API
The callback function is called when a track is signaled by remote side and a new RtpReceiver is created.
The application can tell when tracks are added to the streams by listening to this callback.

BUG=webrtc:6112

Review-Url: https://codereview.webrtc.org/2513063003
Cr-Commit-Position: refs/heads/master@{#16835}
2017-02-24 20:50:48 +00:00
..
2017-02-14 11:07:57 +00:00
2017-02-21 12:19:46 +00:00
2017-02-21 12:19:46 +00:00
2017-02-21 12:19:46 +00:00
2017-02-21 12:19:46 +00:00
2017-02-21 12:19:46 +00:00
2017-02-21 12:19:46 +00:00
2016-07-28 21:53:01 +00:00