SDK / exoplayer

TrackSelector no longer has a listener. Instead, tracks
change events are reported through ExoPlayer.EventListener.
Applications interested in retrieving the selection info
should retrieve it directly from the TrackSelector by
calling an exposed getter.

Pretty sure the ref'd issue is fixed as a side effect of
this change.

Issue: #1942

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=137183073