* Electron Version: 2.0.0
* Operating System (Platform and Version): Fedora 25
* Last known working Electron version:
Didn't tested all previous versions, however the bug is already present in 1.7.8

**Expected Behavior**
I'm currently trying to figure out if a `MenuItem` was triggered through the accelerator. This is possible to achieve through the information available in the `event` object of the `click` callback.

The structure seems to be the following but isn't currently [documented](https://electronjs.org/docs/api/menu-item).

```js
{
  shiftKey: boolean;
  ctrlKey: boolean;
  altKey: boolean;
  metaKey: boolean;
}
```

When a menu item is triggered through the accelerator, the corresponding flags should normally be set to `true`.

**Actual behavior**
This seems to work fine on MacOS. However, on both Windows (10) and Linux (Fedora 25) all this flags are always `false`.

**To Reproduce**
I quickly setup a [repository](https://github.com/njakob/electron-menuitem-bug) to test the current behavior and how to reproduce it.

```sh
$ git clone https://github.com/njakob/electron-menuitem-bug
$ npm install
$ npm start
```
On Fedora 25:
```js
{ shiftKey: false, ctrlKey: false, altKey: false, metaKey: false }
```
While on MacOS:
```js
{ shiftKey: false, ctrlKey: true, altKey: false, metaKey: false }
```
atom/browser/ui/accelerator_util.cc
case ui::VKEY_SHIFT:
        modifiers |= ui::EF_SHIFT_DOWN;
        break;
      case ui::VKEY_CONTROL:
        modifiers |= ui::EF_CONTROL_DOWN;
        break;
      case ui::VKEY_MENU:
        modifiers |= ui::EF_ALT_DOWN;
        break;
      case ui::VKEY_COMMAND:
        modifiers |= ui::EF_COMMAND_DOWN;
        break;
      case ui::VKEY_ALTGR:
        modifiers |= ui::EF_ALTGR_DOWN;
        break;
      
      default:
        key = code;
    }
  }
  if (key == ui::VKEY_UNKNOWN) {
    LOG(WARNING) << shortcut << " doesn't contain a valid key";
    return false;
  }
  *accelerator = ui::Accelerator(key, modifiers);
  SetPlatformAccelerator(accelerator);
  return true;
}
void GenerateAcceleratorTable(AcceleratorTable* table,