DO NOT MERGE WifiMetrics: Record capture duration

Adds a wifi metric that records the capture duration period represented
by the WifiLog proto. This is to improve the way wifiLogs are weighted when
aggregated.
Modified WifiMetrics to use the Clock wrapper of SystemClock to
facilitate unit tests.

BUG=29185886

Change-Id: I61dd2b481c26f0ea21bcb280ce1d40f3d73b7625
5 files changed
tree: 37c9dbe0dd09c22911c54052eb10de47c61df75f
  1. service/
  2. tests/