* 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, v8::Local<v8::Value> val,
    blink::WebDeviceEmulationParams* out) {
  mate::Dictionary dict;
  if (!ConvertFromV8(isolate, val, &dict))
    return false;
  std::string screen_position;
  if (dict.Get("screenPosition", &screen_position)) {
    screen_position = base::ToLowerASCII(screen_position);
    if (screen_position == "mobile")
      out->screenPosition = blink::WebDeviceEmulationParams::Mobile;
    else if (screen_position == "desktop")
      out->screenPosition = blink::WebDeviceEmulationParams::Desktop;
    else
      return false;
  }
  dict.Get("screenSize", &out->screenSize);
  dict.Get("viewPosition", &out->viewPosition);
  dict.Get("deviceScaleFactor", &out->deviceScaleFactor);
  dict.Get("viewSize", &out->viewSize);
  dict.Get("fitToView", &out->fitToView);
  dict.Get("offset", &out->offset);
  dict.Get("scale", &out->scale);
  return true;
}
bool Converter<blink::WebFindOptions>::FromV8(