The graphs don't show any performance bump for
https://codereview.chromium.org/2659623002, which I do see a much better result for
locally. I suspect the function isn't being optimized in turbofan when the
benchmarks run. Maybe this warmup flag will trigger that.

BUG=v8:5895

Review-Url: https://codereview.chromium.org/2664783002
Cr-Commit-Position: refs/heads/master@{#42776}