I'm using `electron.systemPreferences.subscribeNotification` to listen for events coming from `NSDistributedNotificationCenter` in my app:

``` js
prefs.subscribeNotification('com.app.name.EventName', function(notification){
  console.log(notification)
})
```

This produces a single line of output in my log every time the event happens on my system, the only trouble is that the output is `undefined`. My expectation is that I would have access to the `NSNotification` object metadata as JSON.

When I subscribe to this notification in an Objective-C app, I get metadata with the event

``` obj-c
<0x618000000750>-[AppDelegate notify:]: object: com.app.name name: com.app.name.EventName userInfo: {
    Key = Value;
    ...
}
```

atom/browser/api/atom_api_system_preferences.cc
#include "atom/browser/api/atom_api_system_preferences.h"
#include "atom/common/native_mate_converters/callback.h"
#include "atom/common/node_includes.h"
#include "native_mate/dictionary.h"
#if defined(OS_WIN)
#include "ui/base/win/shell.h"
#endif
namespace atom {
namespace api {
SystemPreferences::SystemPreferences(v8::Isolate* isolate) {
  Init(isolate);
}
SystemPreferences::~SystemPreferences() {
}
#if defined(OS_WIN)
bool SystemPreferences::IsAeroGlassEnabled() {
  return ui::win::IsAeroGlassEnabled();
}
#endif
#if !defined(OS_MACOSX)
bool SystemPreferences::IsDarkMode() {
  return false;
}
#endif
mate::Handle<SystemPreferences> SystemPreferences::Create(