Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/36116
[Changelog][Internal]
Add a minimal/reference JavaScript implementation for NativePerformanceObserver - the purpose is both unit testing (JS and native sides separately) and potentially shimming the part of functionality that is not dependent on native side.
This is both a setup for adding general unit tests for the Performance* APIs, but also to be able to do non-trivial changes on JS side for WebPerformance (such as in (D43154319).
Reviewed By: rubennorte
Differential Revision: D43167392
fbshipit-source-id: 213d9534d810dece1dd464f910e92e08dbf39508