Rolling v8/tools/swarming_client to 3db878084b52a5e4eac0a32095e490e1b6ef9526

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

Review URL: https://codereview.chromium.org/1412573002

Cr-Commit-Position: refs/heads/master@{#31320}