The method to handle Timeline updates currently uses
isAd() || isPlaceholder()
to trigger two things:
1. Using the existing requested content position as the content
position.
2. Re-resolving the content position from window to period in case
it changed since the last update.
The condition is correct for case (1) because ads must use the content
position (and not the position in the ad) and a placeholder period must
keep using the requested content position as well until the media
information is no longer a placeholder.
However, case (2) only needs to be done if the content position is
C.TIME_UNSET (to start at the default position) OR if the period is
still a placeholder and we want to re-resolve the position.
The case where re-resolution shouldn't be done is for ads with a non-
placeholder period and a concrete content position. This likely only
affects ads in live stream where the content position is currently
moving with the live stream instead of staying where it is.
PiperOrigin-RevId: 372929439
5167ca65fb