* 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
int bits = 0;
  for (const T& item : vec)
    bits |= item;
  return bits;
}
}  
namespace mate {
template<>
struct Converter<base::char16> {
  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val,
                     base::char16* out) {
    base::string16 code = base::UTF8ToUTF16(V8ToString(val));
    if (code.length() != 1)
      return false;
    *out = code[0];
    return true;
  }
};
template<>
struct Converter<blink::WebInputEvent::Type> {
  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val,