Pass data prop instead of props to _updateViewableItems in _onScroll
Pass data prop instead of props to _updateViewableItems in _onScroll

Summary:
This is a simple bugfix. `_updateViewableItems` expects the `data` prop, as it calls `getItemCount` on it. Without this, `onViewableItemsChanged` updates twice for each scroll position, once from `_onScroll` with the incorrect results, and once from `_updateCellsToRender` with the correct results. This means the callback nigh-on unusable.

I simply logged the results of `onViewableItemsChanged` and made sure they were correct.
Closes https://github.com/facebook/react-native/pull/14162

Differential Revision: D5128363

Pulled By: sahrens

fbshipit-source-id: 3faef812068921a26ed871339da79870fd0d911c

chnfeeeeeef/react-native,chnfeeeeeef/react-native,chnfeeeeeef/react-native,chnfeeeeeef/react-native,chnfeeeeeef/react-native,chnfeeeeeef/react-native,chnfeeeeeef/react-native,chnfeeeeeef/react-native