When seeking to the default position in a period, the containing source may
actually return a position in another period. Multi-period live sources can do
this to seek the player to the live edge.
ExoPlayerImplInternal uses the same functionality when the playback position
reaches the end of a period to determine what period/position to play next.
This means that when playback transitions to a multi-period live source from
some other source (playing a concatenation of those two sources), the player
will play the live edge rather than the beginning of the earliest period.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=128984355
