The way it was before worked, but it's not really documented
that DrmSession methods implemented by DefaultDrmSessionManager
can be called after the session has been released, and it feels
wrong to do this.
At some point we should probably consider moving the DrmSession
part of DefaultDrmSessionManager into an inner class, to force
usage in the "normal" way.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=151003855
