Janic Duplessis 64be88398d Fix content offset validation
Summary:
Content offset was broken because on initial render contentSize is {0,0} so any positive offset is lost. Also inset top/bottom and left/right were inversed �, this led to bad initial scrolling offset when using contentInset. This fixes it by making sure contentSize is actually measured (not {0,0}. I guess it's possible that the content is ACTUALLY {0,0} but in that case I don't think it really matters).

**Test plan**
Tested that a scrollview has proper scroll position when specifying contentOffset. Also tested that it works well with contentInset.
```js
<ScrollView contentOffset={{y: 100}}>
  <View style={{height: 1000}} />
</ScrollView>
```
Closes https://github.com/facebook/react-native/pull/15670

Differential Revision: D5771221

Pulled By: shergin

fbshipit-source-id: 455ed8fd5a4ad1ec61780b573d1a8ef1d77dd124
2017-09-05 16:35:03 -07:00
..
2017-09-05 16:35:03 -07:00