Changes to CLOCK_MONOTONIC as CLOCK_PROCESS_CPUTIME counts only
user time and not kernel time.

BUG=angleproject:892

Change-Id: I3d5aee26ee2bacd7449fdd7795ad8c2b289d7324
Reviewed-on: https://chromium-review.googlesource.com/272652Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>