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This introduces a feature named "VirtualTime" and sets other command line
flags that are required for virtual time if it's enabled.

Change-Id: I0a6d30d9f47f0c59bd8ac815862b74a48448c7a8
Reviewed-on: https://chromium-review.googlesource.com/c/1340538Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609067}