Add counters for true number of events being logged

* The metrics module drops oldest event when event size goes beyond its
  logging capacity
* The understand whether events were dropped, we want to log the true
  number of events.

Bug: 33694310
Test: Code compilation
Change-Id: I381e1cbdf6d08ec2d6e98a53cd27593b700b3d2a
(cherry picked from commit b5633d92)