Summary:
Changelog: [internal]
`ModalHostViewShadowNode` didn't have `RootNodeKit` trait, therefore `getRelativeLayoutMetrics` was including nodes in ancestors that it shouldn't have.
Reviewed By: shergin
Differential Revision: D20735801
fbshipit-source-id: 6b81e3b174c2f82e530abc2bca2da8bebc2270b0