Add CounterMetric and a single use case.

This adds a new class CounterMetric which is used to hold metric
information.  It also adds a single use case for recording and
reporting a counter metric.

BUG: 64001676

Test: Added and ran a new test for the specific CounterMetric use case.
Change-Id: I39cab8328f135e579f80b6c2fab721da5f569795