Summary:
We were using `window.performance` to measure performance. This was because the equivalent node.js API `perf_hooks` wasn't available in the electron version we were using back then.
However, `perf_hooks` has landed in electron meanwhile, so I am moving to this API, as it works for the headless version and jest tests, too.
This allows us to delete the babel transform that was used for node-based tests, where the browser API was replaced with the node API
Reviewed By: jknoxville
Differential Revision: D13860133
fbshipit-source-id: cf1395004fac046dd55751ff465af494173b2cbf
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