SKIPPED can't be handled as CONTENT_RESUME_REQUESTED because after skipping an
ad there may be further ads to play in its ad group.
Remove workaround for handling unexpected playAd without stopAd, as the player
can instead recover when IMA sends CONTENT_RESUME_REQUESTED. This in turn fixes
handling of the case where playAd is called twice but IMA expects only the
first ad to play, when skipping a particular ad. (Add an ad tag where this
occurs to internal samples.)
Check whether a currently playing ad has been marked as played in
ExoPlayerImplInternal, and handle this case as a seek. This ensures that any
loaded ad periods are discarded in the case of CONTENT_RESUME_REQUESTED.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=162610621
07de4d1b2c