[ios] fire onLayout

lib/props.js

@@ -18,6 +18,10 @@ const touchableProps = {
     delayLongPress: PropTypes.number
 };
 
+const layoutProps = {
+    onLayout: PropTypes.func
+};
+
 const responderProps = [
     ...Object.keys(PanResponder.create({}).panHandlers),
     "pointerEvents"
@@ -79,6 +83,7 @@ const pathProps = {
     ...transformProps,
     ...responderProps,
     ...touchableProps,
+    ...layoutProps,
     ...definationProps
 };