GitLab

Allows clients to provide functions to override the return values of
Time::Now(), TimeTicks::Now(), ThreadTicks::Now().

Also adds a way to bypass the override in places where real timestamps
should be used even if an override is set.

Bug: 802217, 751993
Change-Id: I76ce536caf9bf0ef5e580abcc23215ce9851ee34
Reviewed-on: https://chromium-review.googlesource.com/867911
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531923}