Major Description
Zameer has created a new driver implementation around V1Mesos (https://reviews.apache.org/r/57061).
The V1 Mesos code requires a Scheduler callback with a different API. To maximize code reuse, event handling logic was extracted into a MesosCallbackHandler class. However, we do not have the metrics for handling task status update in this class.
Metrics around task status update are key performance indicators for the scheduler. We need to add the metrics back, in order to switch to V1Mesos driver in production.