Add ConditionTimer to CurrentValueBucket struct

Add the update condition timer logic based on state, condition, and
active changes.

Bug: 166159095
Bug: 166158610
Bug: 167458087
Bug: 166639935
Test: `m statsd`
Test: `m statsd_test`
Test: `m`
Test: `atest statsd_test`
Change-Id: If7f0f66d971c6c5d78b1981ff875e466adb19a10