GitLab

This is necessary for using SequenceManager inside
ScopedTaskEnvironment.  It also makes Virtual Time a bit
cleaner from an interface PoV.

Bug: 863341, 891670
Change-Id: Iaa8300b6c4b2f889b4cfe185959e3a280730636d
Reviewed-on: https://chromium-review.googlesource.com/c/1329969
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607254}