We currently don't test if an ad needs to be played in case we are already
playing content.
This is to prevent recreating the current content period when
an ad is marked as skipped. We prefer playing until the designated ad group
position and appending another piece of content. This is less likely to cause
visible discontinuities in case the ad group position is at a key frame
boundary.
However, this means we currently miss updates that require us to play an ad
after a timeline update.
PiperOrigin-RevId: 267553459
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