Rolling v8/buildtools: https://chromium.googlesource.com/chromium/buildtools/+log/9a94713..cb12d6e

TBR=machenbach@chromium.org,vogelheim@chromium.org,hablich@chromium.org

Review-Url: https://codereview.chromium.org/2638693002
Cr-Commit-Position: refs/heads/master@{#42353}