Text: Enabling RCTVirtualText for iOS

Summary:
Without this change native RCTVirtualText module is unactive on iOS.
This can cause bags in Text rendering because failback module (RCTVirtualText) does not popagate dirty status upward.

Depends on D6842304.

Reviewed By: yungsters, AaaChiuuu

Differential Revision: D6854770

fbshipit-source-id: ab8b7acd67309b7351c0074293ee6515a55385ce

Libraries/Text/Text.js

@@ -22,6 +22,7 @@ const ReactNativeViewAttributes = require('ReactNativeViewAttributes');
 const StyleSheetPropType = require('StyleSheetPropType');
 const TextStylePropTypes = require('TextStylePropTypes');
 const Touchable = require('Touchable');
+const UIManager = require('UIManager');
 
 const createReactClass = require('create-react-class');
 const createReactNativeComponentClass = require('createReactNativeComponentClass');
@@ -333,7 +334,7 @@ var RCTText = createReactNativeComponentClass(
 );
 var RCTVirtualText = RCTText;
 
-if (Platform.OS === 'android') {
+if (UIManager.RCTVirtualText) {
   RCTVirtualText = createReactNativeComponentClass('RCTVirtualText', () => ({
     validAttributes: mergeFast(ReactNativeViewAttributes.UIView, {
       isHighlighted: true,