* 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
blink::WebInputEvent::Type* out) {
    std::string type = base::ToLowerASCII(V8ToString(val));
    if (type == "mousedown")
      *out = blink::WebInputEvent::MouseDown;
    else if (type == "mouseup")
      *out = blink::WebInputEvent::MouseUp;
    else if (type == "mousemove")
      *out = blink::WebInputEvent::MouseMove;
    else if (type == "mouseenter")
      *out = blink::WebInputEvent::MouseEnter;
    else if (type == "mouseleave")
      *out = blink::WebInputEvent::MouseLeave;
    else if (type == "contextmenu")
      *out = blink::WebInputEvent::ContextMenu;
    else if (type == "mousewheel")
      *out = blink::WebInputEvent::MouseWheel;
    else if (type == "keydown")
      *out = blink::WebInputEvent::RawKeyDown;
    else if (type == "keyup")
      *out = blink::WebInputEvent::KeyUp;
    else if (type == "char")
      *out = blink::WebInputEvent::Char;