Summary:The animation looks ok now.
However, the original iOS navigator adds transparent overlay and shadow. Any idea how to implement it? I'd like to add it.
Closes https://github.com/facebook/react-native/pull/5061
Differential Revision: D3129246
Pulled By: ericvicenti
fb-gh-sync-id: ee86261a49ea4b8f6854abf69bef3ebfd6878852
fbshipit-source-id: ee86261a49ea4b8f6854abf69bef3ebfd6878852