move augmentClass definition above SyntheticEvent Proxy replacement (#10011)

src/renderers/shared/stack/event/SyntheticEvent.js

@@ -210,6 +210,33 @@ Object.assign(SyntheticEvent.prototype, {
 
 SyntheticEvent.Interface = EventInterface;
 
+/**
+ * Helper to reduce boilerplate when creating subclasses.
+ *
+ * @param {function} Class
+ * @param {?object} Interface
+ */
+SyntheticEvent.augmentClass = function(Class, Interface) {
+  var Super = this;
+
+  var E = function() {};
+  E.prototype = Super.prototype;
+  var prototype = new E();
+
+  Object.assign(prototype, Class.prototype);
+  Class.prototype = prototype;
+  Class.prototype.constructor = Class;
+
+  Class.Interface = Object.assign({}, Super.Interface, Interface);
+  Class.augmentClass = Super.augmentClass;
+
+  PooledClass.addPoolingTo(Class, PooledClass.fourArgumentPooler);
+};
+
+/** Proxying after everything set on SyntheticEvent
+  * to resolve Proxy issue on some WebKit browsers
+  * in which some Event properties are set to undefined (GH#10010)
+  */
 if (__DEV__) {
   if (isProxySupported) {
     /*eslint-disable no-func-assign */
@@ -243,28 +270,6 @@ if (__DEV__) {
     /*eslint-enable no-func-assign */
   }
 }
-/**
- * Helper to reduce boilerplate when creating subclasses.
- *
- * @param {function} Class
- * @param {?object} Interface
- */
-SyntheticEvent.augmentClass = function(Class, Interface) {
-  var Super = this;
-
-  var E = function() {};
-  E.prototype = Super.prototype;
-  var prototype = new E();
-
-  Object.assign(prototype, Class.prototype);
-  Class.prototype = prototype;
-  Class.prototype.constructor = Class;
-
-  Class.Interface = Object.assign({}, Super.Interface, Interface);
-  Class.augmentClass = Super.augmentClass;
-
-  PooledClass.addPoolingTo(Class, PooledClass.fourArgumentPooler);
-};
 
 PooledClass.addPoolingTo(SyntheticEvent, PooledClass.fourArgumentPooler);