* 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
if (!dict.Get("keyCode", &str))
    return false;
  bool shifted = false;
  ui::KeyboardCode keyCode = atom::KeyboardCodeFromStr(str, &shifted);
  out->windowsKeyCode = keyCode;
  if (shifted)
    out->modifiers |= blink::WebInputEvent::ShiftKey;
  ui::DomCode domCode = ui::UsLayoutKeyboardCodeToDomCode(keyCode);
  out->domCode = static_cast<int>(domCode);
  ui::DomKey domKey;
  ui::KeyboardCode dummy_code;
  int flags = atom::WebEventModifiersToEventFlags(out->modifiers);
  if (ui::DomCodeToUsLayoutDomKey(domCode, flags, &domKey, &dummy_code))
    out->domKey = static_cast<int>(domKey);
  if ((out->type == blink::WebInputEvent::Char ||
       out->type == blink::WebInputEvent::RawKeyDown)) {
    
    
    size_t text_length_cap = blink::WebKeyboardEvent::textLengthCap;
    base::string16 text16 = base::UTF8ToUTF16(str);
    memset(out->text, 0, text_length_cap);
    memset(out->unmodifiedText, 0, text_length_cap);
    for (size_t i = 0; i < std::min(text_length_cap, text16.size()); ++i) {
      out->text[i] = text16[i];
      out->unmodifiedText[i] = text16[i];
    }
  }
  return true;
}
bool Converter<content::NativeWebKeyboardEvent>::FromV8(