* Electron version: 1.4.4
* Operating system: win10

Hi,
Example described [here](https://github.com/electron/electron/blob/master/docs/api/global-shortcut.md) works with v1.4.0 but doesn't seem to work with v1.4.4 or v1.4.5.  Method `globalShortcut.isRegistered ` returns true, but the callback isn't called. 

Thanks!
atom/browser/api/atom_api_system_preferences_win.cc
invertered_color_scheme_ = IsInvertedColorScheme();
  WNDCLASSEX window_class;
  base::win::InitializeWindowClass(
      kSystemPreferencesWindowClass,
      &base::win::WrappedWindowProc<SystemPreferences::WndProcStatic>,
      0, 0, 0, NULL, NULL, NULL, NULL, NULL,
      &window_class);
  instance_ = window_class.hInstance;
  atom_ = RegisterClassEx(&window_class);
  
  
  
  
  window_ = CreateWindow(MAKEINTATOM(atom_),
                         0, WS_POPUP, 0, 0, 0, 0, 0, 0, instance_, 0);
  gfx::CheckWindowCreated(window_);
  gfx::SetWindowUserData(window_, this);
}
LRESULT CALLBACK SystemPreferences::WndProcStatic(HWND hwnd,
                                              UINT message,
                                              WPARAM wparam,
                                              LPARAM lparam) {
  SystemPreferences* msg_wnd = reinterpret_cast<SystemPreferences*>(
      GetWindowLongPtr(hwnd, GWLP_USERDATA));
  if (msg_wnd)
    return msg_wnd->WndProc(hwnd, message, wparam, lparam);
  else
    return ::DefWindowProc(hwnd, message, wparam, lparam);
}
LRESULT CALLBACK SystemPreferences::WndProc(HWND hwnd,