This fixes false positive data race reported by TSAN.

Bug: chromium:790004
Change-Id: I6335af1735fe9ea77a26cc9919ec4f089b004cdf
Reviewed-on: https://chromium-review.googlesource.com/800936Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49766}