Summary:
[Changelog][Internal]
This adds module specs for the native part of PerformanceObserver, as well as the interaction logic vs the NativePerformanceObserver API.
See https://fb.quip.com/MdqgAk1Eb2dV for more detail.
Reviewed By: rubennorte
Differential Revision: D40897006
fbshipit-source-id: 77475f21dad9ee9dbe15df5a989eb08d314e6db2