* 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::WebMouseWheelEvent* out) {
  mate::Dictionary dict;
  if (!ConvertFromV8(isolate, val, &dict))
    return false;
  if (!ConvertFromV8(isolate, val, static_cast<blink::WebMouseEvent*>(out)))
    return false;
  dict.Get("deltaX", &out->deltaX);
  dict.Get("deltaY", &out->deltaY);
  dict.Get("wheelTicksX", &out->wheelTicksX);
  dict.Get("wheelTicksY", &out->wheelTicksY);
  dict.Get("accelerationRatioX", &out->accelerationRatioX);
  dict.Get("accelerationRatioY", &out->accelerationRatioY);
  dict.Get("hasPreciseScrollingDeltas", &out->hasPreciseScrollingDeltas);
#if defined(USE_AURA)
  
  bool can_scroll = true;
  if (dict.Get("canScroll", &can_scroll) && !can_scroll) {
    out->hasPreciseScrollingDeltas = false;
    out->modifiers &= ~blink::WebInputEvent::ControlKey;
  }
#endif
  return true;
}
bool Converter<blink::WebFloatPoint>::FromV8(