Bug 1073033 - Add forEach benchmarks.

These micro benchmarks are comparing the performance of a simple for-loop written by hand against, a custom implementation of forEach which does not handle errors, and the implementation of forEach which is part of the self-hosted function.

The goal of these 3 benchmarks is to make sure that new primitive functions of JavaScript are as fast as hand-written code, and ensure that any custom polyfill would be as fast as the self-hosted version.

These benchmarks are running in about 30 to 70 ms each.