Make ratchet.FileTouchedCondition resilient to NTP changes.

NTP servers or other things may adjust the system clock, which means
we can't rely on mtime to increase when a file is touched, or compare
it to other times.  Simplify FileTouchedCondition just to look for
changed mtimes.

BUG=32072505

Change-Id: Ieb7a39c549b5525554f1a3df547f14d80b2187d8
2 files changed