Github user aljoscha commented on the issue:
https://github.com/apache/flink/pull/5092
The change looks good, but I would like the metrics to be called
`currentInputWatermark` and `currentOutputWatermark`. We will likely have that
distinction in more places in the future and @zentol pointed out to me that the
`AsyncWaitOperator` already has differing input and output watermarks.---
