This flag is intended as a staging flag for TurboFan. It serves as a
single flag that always enables a most recent configuration of TurboFan
for test suites and benchmarks, without needing to update test drivers.

R=titzer@chromium.org,machenbach@chromium.org

Review URL: https://codereview.chromium.org/1094573002

Cr-Commit-Position: refs/heads/master@{#27896}