Using the new getNextWindowIndex method of Timeline, LoopingMediaSource now
uses a InfinitelyLoopingTimeline which does not unroll the windows to
157 million iterations but just starts from the beginning. If an explicit
number of iterations is given, we still unroll.
This change also allows multi-window timebars to show infinitely looping
playlists correctly.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=154817554
ab30d715c7