The ad events are independent of the other media source events. Also,
registering the listener to the internal ad media sources will report the
regular media source events twice: once directly (with a non-ad media period
id) and once through the wrapping ads source (with the correct ad media period
id).
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=189905561
