Warmup runs

[nolanlawson]

One issue we have in some projects (LDS, Locker) is that we see a big perf difference between the first few iterations and the next n. Most likely this is because the JavaScript engine is doing some JITing, so the first few iterations are measuring the unJITed performance.

Ideally, Best would have a setting to do some number of warmup runs, so we could consistently measure peak performance (i.e. JITed performance).

The alternative (to try to measure only un-JITed performance) is technically possible but unfeasible in practice, since it would mean closing the tab and clearing the browser cache between each iteration (in the worst case – it depends on how aggressive browsers are about caching).