Move AddTrack stats update to submethod
Move AddTrack stats update to submethod

AddTrack is just a legacy wrapper for the new AddTrack method, so
calling the new AddTrack method should do everything that the old one
does.

Bug: None
Change-Id: I272a9e9584c470d54243377c1307b786f41c660d
Reviewed-on: https://webrtc-review.googlesource.com/37546
Reviewed-by: Peter Thatcher <86dc5d06abaeadbc7f61dd701fafcbca29ff9bbc@webrtc.org>
Commit-Queue: Steve Anton <93f73658da16553b94c040887a439a155812e54e@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21508}
ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc