### Issue Details

* **Electron Version:**
  * 3.0.x, 4.0.x, 5.0.x, 6.0.x
* **Operating System:**
  * macOS 10.14.5
* **Last Known Working Electron version:**
  * 2.0.x

### Expected Behavior
`BrowserWindow.on('swipe')` fires when doing a 3-finger swipe gesture.

### Actual Behavior
`BrowserWindow.on('swipe')` does not fire.

shell/browser/api/atom_api_browser_window.cc
if (api_web_contents_)
    api_web_contents_->RemoveObserver(this);
  
  
  if (web_contents())
    Cleanup();
}
void BrowserWindow::OnInputEvent(const blink::WebInputEvent& event) {
  switch (event.GetType()) {
    case blink::WebInputEvent::kGestureScrollBegin:
    case blink::WebInputEvent::kGestureScrollUpdate:
    case blink::WebInputEvent::kGestureScrollEnd:
      Emit("scroll-touch-edge");
      break;
    default:
      break;
  }
}
void BrowserWindow::RenderViewHostChanged(content::RenderViewHost* old_host,
                                          content::RenderViewHost* new_host) {
  if (old_host)
    old_host->GetWidget()->RemoveInputEventObserver(this);
  if (new_host)
    new_host->GetWidget()->AddInputEventObserver(this);
}
void BrowserWindow::RenderViewCreated(