Remove another use of atomicops.

R=mstarzinger@chromium.org

Bug: v8:8834
Change-Id: Ide1aa87f4bb4cdc4346fe7b1bf78b8118592c7ae
Reviewed-on: https://chromium-review.googlesource.com/c/1491603
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59935}