Resolve the media period for ad playback when resolving a subsequent period and
when receiving a timeline where the playing period in range (but wasn't before).
Fix the seek position calculation when a current ad must be skipped and is
followed by another ad.
Check MediaPeriodInfos match when checking MediaPeriodHolders, to handle cases
where a future ad should no longer be played. This may involve playing two
content media periods consecutively.
Issue: #3584
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Created by MOE: https://github.com/google/moe
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