In order to clean up potentially bad BillingEvent.Recurring expansions, we'll need to be able to trace synthetic billing events back to particular runs of the []. This field will be set to the cursor time at the start of the MR (all expansions in one MR job will have the same timestamp).
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=121999938
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