If there are many workers and we are very unlucky, the cmpxchg loop can
in fact fail for more than 5 times. This CL removes this unneeded
limitation to avoid spurious failures.

R=mstarzinger@chromium.org

Bug: chromium:824443
Change-Id: I0a6adde1330c8a8389a42b36bf44e516fae8c574
Reviewed-on: https://chromium-review.googlesource.com/1213170Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55749}