Override onContentSizeChange prop on ScrollView before rendering

Summary:
We got a report that onContentSizeChange function was being called with an object instead of a number for width, sometimes. Upon debugging, it looked like the param being passed in was a native event wrapper. Tim eventually figured out that this is because there's a TextInput child, and the event bubbles: diffusion/FBS/browse/master/fbobjc/Libraries/FBReactKit/js/react-native-github/Libraries/Text/RCTTextViewManager.m;afbdef32df50$39

Because ScrollView just passes all its props down to the component it eventually renders (RCTScrollView on iOS), the TextInput event bubbles up and triggers the onContentSizeChange prop that was passed in directly, instead of going through the layer in ScrollView that normally unpacks width/height from the native event: diffusion/FBS/browse/master/fbobjc/Libraries/FBReactKit/js/react-native-github/Libraries/Components/ScrollView/ScrollView.js;247ddb2022151b68dd9f83a888b6e0ec9923737a$413-416

Overriding the prop before passing down to RCTScrollView will break that chain, so that the event will continue to bubble but it won't find the incorrect prop from ScrollView.

Reviewed By: yungsters

Differential Revision: D3999689

fbshipit-source-id: d6c3bf711969b3e1c6fc1e51fd44c6894910bc3d

Libraries/Components/ScrollView/ScrollView.js

@@ -475,6 +475,9 @@ const ScrollView = React.createClass({
       alwaysBounceHorizontal,
       alwaysBounceVertical,
       style: ([baseStyle, this.props.style]: ?Array<any>),
+      // Override the onContentSizeChange from props, since this event can
+      // bubble up from TextInputs
+      onContentSizeChange: null,
       onTouchStart: this.scrollResponderHandleTouchStart,
       onTouchMove: this.scrollResponderHandleTouchMove,
       onTouchEnd: this.scrollResponderHandleTouchEnd,