dumpsys: report per-service dump times

In WiFi soak testing, we've seen several cases where
dumpsys times out. We've been unable to pin down the
cause of the timeouts, as there's no single service
that is obviously hung.

Add reporting of service dump times, to help figure
out why dumpsys is timing out.

BUG=29090949
TEST=manual

Manual test
- load build on bullhead
$ adb shell dumpsys | grep 'was the duration'
- see non-zero values

Change-Id: Iaba60d840ac55cba171a3ccbc74c2aee8b23dce6