Bench frame time instead if op/s

[krispya]

For live applications like video games it would be really useful to bench frame time instead of op/s. Where frame time is how much ms it takes to execute the test per requestAnimationFrame. This also gives a better idea of how V8 will optimize the code in a real world scenario where it may take a couple frames for it to get flagged as a hot path.

[Llorx]

@krispya I can add a configurable output. Can you show me an example of what do you expect?