* **Electron Version:**
  * 5.0.x
* **Operating System:**
  * macOS 10.14.5

### Expected Behavior
Electron does not crash at exit.

### Actual Behavior
The notifications are sent well, i use the close() function to avoid persistence in Notification Center. 

By doing this every time I quit the application I have a message that warns me that the application did not stop properly.

### To Reproduce
```javascript
const notif = new Notification({title: title, body: body, silent: true})
notif.on('click', () => appEvent.emit('show-window'))
notif.show()
setTimeout(() => notif.close(), 10000)
```
After sending notification(s), close application (app.quit()) and the error will appear.

To no longer have the error after quitting app, i do not use the function close () but my application generates a lot of notifications and I would have preferred to handle that.

shell/browser/api/atom_api_notification.cc
const std::vector<electron::NotificationAction>& actions) {
  actions_ = actions;
}
void Notification::SetCloseButtonText(const base::string16& text) {
  close_button_text_ = text;
}
void Notification::NotificationAction(int index) {
  Emit("action", index);
}
void Notification::NotificationClick() {
  Emit("click");
}
void Notification::NotificationReplied(const std::string& reply) {
  Emit("reply", reply);
}
void Notification::NotificationDisplayed() {
  Emit("show");
}
void Notification::NotificationDestroyed() {}
void Notification::NotificationClosed() {
  Emit("close");
}
void Notification::Close() {
  if (notification_) {
    notification_->Dismiss();
    notification_.reset();
  }
}
void Notification::Show() {