This class provides byte level CAS operation using word level CAS.

Bug: chromium:694255
Change-Id: I39e661ee8d11e3f61fd5cb64c36f8f5ee94d1244
Reviewed-on: https://chromium-review.googlesource.com/612170
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47311}