Standard Flow type for style prop

Reviewed By: sahrens

Differential Revision: D5978082

fbshipit-source-id: bd251ed3ecc1f15595e2f5ee941e3865a225c1fd

Author: frantic

Libraries/StyleSheet/StyleSheet.js

@@ -20,6 +20,8 @@ const flatten = require('flattenStyle');
 
 export type Styles = {[key: string]: Object};
 export type StyleSheet<S: Styles> = {[key: $Keys<S>]: number};
+export type StyleValue = {[key: string]: Object} | number | false | null;
+export type StyleProp = StyleValue | Array<StyleValue>;
 
 let hairlineWidth = PixelRatio.roundToNearestPixel(0.4);
 if (hairlineWidth === 0) {