Summary:
Tried to automate this with [cjs-to-es6](https://github.com/nolanlawson/cjs-to-es6) but it only
works on vanilla JS files without any special Flow syntax. I converted some places
manually but we can just do the rest as we modify the files.
Reviewed By: jknoxville
Differential Revision: D16340187
fbshipit-source-id: b55c7ce2d719876e47e85f5f3fce13b8c8ae4010