While the timeline is empty, we keep a dummy MediaPeriodId in PlaybackInfo with
a period index of 0. We leak this MediaPeriodId in actual use in these
situations:
1. When issuing an IllegalSeekPosition after preparation. The timeline becomes
non-empty, but the media period id stays at its dummy value.
2. When re-adding sources to a previously empty timeline. The dummy period id
is used as the start position for the new non-empty timeline.
This change makes:
- the constructor of PlaybackInfo using those dummy values more explicit
- prevents the issues above by using the correct default position in the new
non-empty timeline for the above mentioned cases.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=205803006
