Summary:
Yoga layout can be invoked on multiple threads, and gCurrentGenerationCount is a shared global without synchronization.
Changelog: [General] [Fixed] - Fix an internal thread safety issue in Yoga
Reviewed By: SidharthGuglani
Differential Revision: D18092734
fbshipit-source-id: 85753d139549b4e5507f97a56d589fb6854557fa