[JobQueue] Added per-type stat counter calls for better graphs.

* Also refactored doBatchPush() for the DB job queue to reduce
  the amount of PHP closure work-arounds. I'd rather not add a
  $type variable to the bloated 'use' clause.

Change-Id: I265effc061558d96048dcc331ac2338a8b95aff5
Merge "[JobQueue] Added per-type stat counter calls for better graphs."