* Electron version: 1.4.15
* Operating system: Windows 10

### Expected behavior

The new [before-input-event](https://github.com/electron/electron/blob/master/docs/api/web-contents.md#event-before-input-event) event should imitate the properties from [KeyboardEvents](https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent).

### Actual behavior

Missing the ```KeyboardEvent.code``` equivalent.
Because of this, it's not possible for me to distinguish between my shortcuts created with 1 and Numpad1 for instance.

Looking at comments for the ```before-input-event``` issue ([#7586](https://github.com/electron/electron/issues/7586#issuecomment-263431783)), The ```code``` property was never mentioned in the psudo code. Missed by mistake?

```code``` is available on the ```keydown``` events in Electron, which I use now. I'm not able to rewrite my code to use ```before-input-event```, for now.
atom/common/native_mate_converters/blink_converter.cc
v8::Isolate* isolate, const blink::WebContextMenuData::MediaType& in) {
  switch (in) {
    case blink::WebContextMenuData::MediaTypeImage:
      return mate::StringToV8(isolate, "image");
    case blink::WebContextMenuData::MediaTypeVideo:
      return mate::StringToV8(isolate, "video");
    case blink::WebContextMenuData::MediaTypeAudio:
      return mate::StringToV8(isolate, "audio");
    case blink::WebContextMenuData::MediaTypeCanvas:
      return mate::StringToV8(isolate, "canvas");
    case blink::WebContextMenuData::MediaTypeFile:
      return mate::StringToV8(isolate, "file");
    case blink::WebContextMenuData::MediaTypePlugin:
      return mate::StringToV8(isolate, "plugin");
    default:
      return mate::StringToV8(isolate, "none");
  }
}
v8::Local<v8::Value> Converter<blink::WebContextMenuData::InputFieldType>::ToV8(