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.
const shouldBeReleasedProperties = [
  'dispatchConfig',
  '_targetInst',
  'nativeEvent',
  'isDefaultPrevented',
  'isPropagationStopped',
  '_dispatchListeners',
  '_dispatchInstances',
];
/**
 * @interface Event
 * @see http://www.w3.org/TR/DOM-Level-3-Events/
 */
const EventInterface = {
  type: null,
  target: null,
  
  currentTarget: function() {
    return null;
  },
  eventPhase: null,
  bubbles: null,
  cancelable: null,
  timeStamp: function(event) {
    return event.timeStamp || Date.now();
  },
  defaultPrevented: null,
  isTrusted: null,
};
function functionThatReturnsTrue() {