Previously the ad/content progress updates were toggled based on whether the
player was playing ads or content. After this change, we switch based on
whether playAd/stopAd has been called instead.
This seems to resolve an issue where occasionally the player would get stuck at
the start of an ad, but as I don't have a root cause for that issue and it's
only sporadically reproducible I'm not certain this is a reliable fix.
Issue: #3525
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=179169296
