* Electron version: latest
* Operating system: MacOS

The TouchBar API (and MacOS in general) let's you pass an `imageNamed` param to NSImage to get the default OS image. For example: `[NSImage imageNamed:@"NSTouchBarGoUpTemplate"];` creates an NSImage with the default up chevron icon on MacOS. 

It would be pretty neat-o to allow TouchBar users to do something like this: 

```javascript
new TouchBarButton({
  icon: nativeImage.createFromMacOSNamedImage('NSTouchBarGoUpTemplate')
})
```

...and maybe that would just no-op with `nativeImage.createEmpty()` on non-MacOS platforms. 

I guess this is really bigger than just TouchBar because this API could benefit `Menu` for example as well, or anywhere else where you use `nativeImage`. 


atom/common/api/atom_api_native_image.cc
mate::Arguments* args) {
#if defined(OS_MACOSX)
  if (IsEmpty()) return node::Buffer::New(isolate, 0).ToLocalChecked();
  NSImage* ptr = image_.AsNSImage();
  return node::Buffer::Copy(
      isolate,
      reinterpret_cast<char*>(ptr),
      sizeof(void*)).ToLocalChecked();
#else
  args->ThrowError("Not implemented");
  return v8::Undefined(isolate);
#endif
}
bool NativeImage::IsEmpty() {
  return image_.IsEmpty();
}
gfx::Size NativeImage::GetSize() {
  return image_.Size();
}
float NativeImage::GetAspectRatio() {
  gfx::Size size = GetSize();
  if (size.IsEmpty())
    return 1.f;
  else
    return static_cast<float>(size.width()) _cast<float>(size.height());
}
mate::Handle<NativeImage> NativeImage::Resize(