Create locally runnable benchmark suite adapted from jsperf code.

(Moved from #356)

Run the task with `grunt runBenchmark`. You should see a jsperf clone adapted for our needs. 

I took the example code from benchmark.js and adapted it to be a lot friendlier. The API key set at the bottom of `benchmark.html` is generated from a free account on browserscope. 

I think this is a nice addition to the project and possibly something we could add to layoutmanager.org. If we had a way to automatically version the browserscope keys we could easily check for performance regressions.

This suite contains 4 (slow) benchmarks so far.