Add eslint benchmark

[mathiasbynens]

[alopezsanchez]

I'll work on it!

[mathiasbynens]

Hey @alopezsanchez, did you make any progress? No worries if not, just checking in.

Note that ESLint uses Espree as its parser nowadays, and Espree is already included in the benchmark.

[matthewnbrown]

@mathiasbynens I'll try to add it. I'm pretty new to this though.

[mathiasbynens]

@everspy Thanks for taking a look! Btw, https://github.com/v8/web-tooling-benchmark/blob/master/CONTRIBUTING.md might be helpful, in case you hadn't seen it.