Create performance benchmarks

[lucaswoj]

We should create some performance benchmarks for mapbox-gl-draw that are quantifiable and repeatable.

Ideally, these benchmarks would be runnable in a headless environment using something like http://karma-runner.github.io.

It probably makes sense to work on the upstream mapbox-gl-js performance benchmarks first, and use the lessons and infrastructure from those to build the mapbox-gl-draw benchmarks.

ref mapbox/mapbox-gl-js#954
ref mapbox/mapbox-gl-js#1362

[mcwhittemore]

Like tests, should these use mapbox-gl-js or mapbox-gl-js-mock? Using a mock would let us know the perf of gl-draw. Using the real thing, would help us catch when gl-draw is using a slow gl-js function.

[lucaswoj]

The performance tests should use the real mapbox-gl-js.

[lucaswoj]

Highly relevant stuff moving in mapbox/mapbox-gl-js#2231