* 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
#include "atom/common/native_mate_converters/blink_converter.h"
#include <algorithm>
#include <string>
#include <vector>
#include "atom/common/keyboard_util.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "content/public/browser/native_web_keyboard_event.h"
#include "native_mate/dictionary.h"
#include "third_party/WebKit/public/web/WebCache.h"
#include "third_party/WebKit/public/web/WebDeviceEmulationParams.h"
#include "third_party/WebKit/public/web/WebFindOptions.h"
#include "third_party/WebKit/public/web/WebInputEvent.h"
#include "ui/base/clipboard/clipboard.h"
#include "ui/events/keycodes/dom/keycode_converter.h"
#include "ui/events/keycodes/keyboard_code_conversion.h"
namespace {
template<typename T>
int VectorToBitArray(const std::vector<T>& vec) {