* Electron version: 1.4.14
* Operating system: Windows 8.1

### Expected behavior

A fullscreen transparent window should be transparent.

### Actual behavior

The window is not transparent (has a white background).

### How to reproduce

```
electron.app.on("ready", function () {
    var win = new BrowserWindow({
        show: true,
        frame: false,
        fullscreen: true,
        transparent: true
    });
});
```

Refs https://github.com/electron/electron/issues/8321#issuecomment-273615701


atom/browser/native_window_views.cc
return window_->GetNativeWindow();
}
void NativeWindowViews::SetProgressBar(
    double progress, NativeWindow::ProgressState state) {
#if defined(OS_WIN)
  taskbar_host_.SetProgressBar(GetAcceleratedWidget(), progress, state);
#elif defined(USE_X11)
  if (unity::IsRunning()) {
    unity::SetProgressFraction(progress);
  }
#endif
}
void NativeWindowViews::SetOverlayIcon(const gfx::Image& overlay,