Summary:
The `shouldComponentUpdate` policies were meant to be a built-in optimization, but it prevents rendering at unexpected times, which has been causing confusion. Apps can use normal react optimization techniques to avoid extra rendering- Navigation will no longer attempt to optimize the render tree
Addresses https://github.com/facebook/react-native/issues/7720
Reviewed By: hedgerwang
Differential Revision: D3649735
fbshipit-source-id: 9461620445a6a57a1635113df7ec4026c0d6b9d2