connect mediametrics service to statsd

take the collected media.metrics (as they arrive) and push a copy over
to statsd, the statistics logging subsystem.
gather data, wrap in protobufs apppropriately, and submit it to statsd.

Bug: 118782504
Test: statsd's test_drive app
Change-Id: Ieb82c43633851075e9eaf65d2a95c8cba87441ea