Summary:
This is necessary to fix an extraneous warning when a VirtualizedList is constructed on the first frame.
On the first frame, the dt is huge (ie, time since epoch).
On the second frame (which may legitimately be slow as a result of a lot to render), it will then assume there were two consecutive slow frames, and print a warning:
"VirtualizedList: You have a large list that is slow to update..."
Closes https://github.com/facebook/react-native/pull/14393
Differential Revision: D5210467
Pulled By: sahrens
fbshipit-source-id: 2e79218c3d66a4a9df4884f328a125047ef264ed
5840a9051d