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.
});
    Object.defineProperty(event, 'returnValue', {
      get() {
        return false;
      },
    });
    node.dispatchEvent(event);
    expect(expectedCount).toBe(2);
  });
  it('should be able to `stopPropagation`', () => {
    let node;
    let expectedCount = 0;
    const eventHandler = syntheticEvent => {
      expect(syntheticEvent.isPropagationStopped()).toBe(false);
      syntheticEvent.stopPropagation();
      expect(syntheticEvent.isPropagationStopped()).toBe(true);
      expectedCount++;
    };
    node = ReactDOM.render(<div onClick={eventHandler} />, container);
    const event = document.createEvent('Event');
    event.initEvent('click', true, true);
    node.dispatchEvent(event);
    expect(expectedCount).toBe(1);
  });
  it('should be able to `persist`', () => {
    let node;
    let expectedCount = 0;
    let syntheticEvent;