I think maybe we should revert https://github.com/facebook/react/pull/5947.

People already think `proxyEvent` is some kind of an API: https://github.com/facebook/react/issues/12169.

It's also annoying to view in the debugger because none of the properties show up.

Instead, we could seal the event object or something like that.
return Super.apply(this, arguments);
  }
  Object.assign(prototype, Class.prototype);
  Class.prototype = prototype;
  Class.prototype.constructor = Class;
  Class.Interface = Object.assign({}, Super.Interface, Interface);
  Class.extend = Super.extend;
  addEventPoolingTo(Class);
  return Class;
};
/** 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__) {
  const isProxySupported =
    typeof Proxy === 'function' &&
    
    !Object.isSealed(new Proxy({}, {}));
  if (isProxySupported) {
    
    SyntheticEvent = new Proxy(SyntheticEvent, {
      construct: function(target, args) {
        return this.apply(target, Object.create(target.prototype), args);
      },
      apply: function(constructor, that, args) {
        return new Proxy(constructor.apply(that, args), {
          set: function(target, prop, value) {
            if (
              prop !== 'isPersistent' &&