Avoiding the helper function to get the time in milliseconds avoids
redundantly getting the current platform and simplifies code.

R=mstarzinger@chromium.org

Bug: v8:8916
Change-Id: Ie7214f896a14f45aef359ea095a4b0532aeccf77
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1561070
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60744}