This makes live byte count updates on the main thread non-atomic.

Bug: chromium:694255
TBR: mlippautz@chromium.org
Change-Id: I84da2b0647f63ad9d8f2be757d305d58945a00ff
Reviewed-on: https://chromium-review.googlesource.com/613623
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47468}