* **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
#include "shell/browser/api/atom_api_notification.h"
#include "base/guid.h"
#include "base/strings/utf_string_conversions.h"
#include "shell/browser/api/atom_api_menu.h"
#include "shell/browser/atom_browser_client.h"
#include "shell/browser/browser.h"
#include "shell/common/gin_converters/image_converter.h"
#include "shell/common/gin_helper/dictionary.h"
#include "shell/common/gin_helper/object_template_builder.h"
#include "shell/common/node_includes.h"
#include "url/gurl.h"
namespace gin {
template <>
struct Converter<electron::NotificationAction> {
  static bool FromV8(v8::Isolate* isolate,