* 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::Modifiers* out) {
    std::string modifier = base::ToLowerASCII(V8ToString(val));
    if (modifier == "shift")
      *out = blink::WebInputEvent::ShiftKey;
    else if (modifier == "control" || modifier == "ctrl")
      *out = blink::WebInputEvent::ControlKey;
    else if (modifier == "alt")
      *out = blink::WebInputEvent::AltKey;
    else if (modifier == "meta" || modifier == "command" || modifier == "cmd")
      *out = blink::WebInputEvent::MetaKey;
    else if (modifier == "iskeypad")
      *out = blink::WebInputEvent::IsKeyPad;
    else if (modifier == "isautorepeat")
      *out = blink::WebInputEvent::IsAutoRepeat;
    else if (modifier == "leftbuttondown")
      *out = blink::WebInputEvent::LeftButtonDown;
    else if (modifier == "middlebuttondown")
      *out = blink::WebInputEvent::MiddleButtonDown;
    else if (modifier == "rightbuttondown")
      *out = blink::WebInputEvent::RightButtonDown;
    else if (modifier == "capslock")
      *out = blink::WebInputEvent::CapsLockOn;
    else if (modifier == "numlock")
      *out = blink::WebInputEvent::NumLockOn;
    else if (modifier == "left")
      *out = blink::WebInputEvent::IsLeft;
    else if (modifier == "right")
      *out = blink::WebInputEvent::IsRight;
    return true;
  }