* Electron version: 2.0.0-beta.7
* Operating system: macOS 10.13.4

### Expected behavior

<!-- What do you think should happen? -->
When HTML fullscreen mode is active, exiting fullscreen on the window level (clicking the green button or calling `win.setFullScreen(false)` should also exit HTML fullscreen mode.

### Actual behavior

HTML fullscreen mode stays active. Chrome correctly exits HTML fullscreen mode.

### How to reproduce

Use console in the default_app:

```
document.addEventListener('webkitfullscreenchange', () => console.log('webkitfullscreenchange'));
document.documentElement.webkitRequestFullscreen();
```

now exit fullscreen by clicking the green button or run `require('electron').remote.getCurrentWindow().setFullScreen(false);`

Compare to what happens when you do the same in Chrome/Chromium
`webkitfullscreenchange` should be logged twice (once for enter, once for exit)
`document.webkitFullscreenElement` should also be `null`

Possible workaround is:
```
win.on('leave-full-screen', () => {
  win.webContents.executeJavaScript('document.webkitExitFullscreen();');
});
```

atom/browser/api/atom_api_browser_window.cc
if (!window_unresponsive_closure_.IsCancelled())
    return;
  window_unresponsive_closure_.Reset(
      base::Bind(&BrowserWindow::NotifyWindowUnresponsive, GetWeakPtr()));
  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
      FROM_HERE, window_unresponsive_closure_.callback(),
      base::TimeDelta::FromMilliseconds(ms));
}
void BrowserWindow::NotifyWindowUnresponsive() {
  window_unresponsive_closure_.Cancel();
  if (!window_->IsClosed() && window_->IsEnabled() &&
      !IsUnresponsiveEventSuppressed()) {
    Emit("unresponsive");
  }
}
void BrowserWindow::Cleanup() {
  auto* host = web_contents()->GetRenderViewHost();
  if (host)
    host->GetWidget()->RemoveInputEventObserver(this);
  api_web_contents_->DestroyWebContents(true );
  Observe(nullptr);
}
mate::WrappableBase* BrowserWindow::New(mate::Arguments* args) {