This flag is on by default but it will allow us to turn that off in
favor of harmony-sloppy in the future.

BUG=v8:3305, v8:2198
LOG=N
R=littledan@chromium.org, rossberg@chromium.org

Review URL: https://codereview.chromium.org/1218803006

Cr-Commit-Position: refs/heads/master@{#29526}