StateTracker handles active state changes

When a state change occurs, metrics should only make certain updates if
the metric is active. This is already handled in CountMetricProducer and
DurationMetricProducer. In ValueMetricProducer, we will return
immediately if the metric is not active during a state change.

Test: m statsd_test && adb sync data && adb shell
data/nativetest/statsd_test/statsd_test
Bug: b/153101724

Change-Id: Ib2a96600a0f1acec054638515d606716cf0ca6b6