* 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
brightray::InspectableWebContents* web_contents,
    const mate::Dictionary& options,
    NativeWindow* parent)
    : NativeWindow(web_contents, options, parent),
      window_(new views::Widget),
      web_view_(inspectable_web_contents()->GetView()->GetView()),
      menu_bar_autohide_(false),
      menu_bar_visible_(false),
      menu_bar_alt_pressed_(false),
#if defined(OS_WIN)
      checked_for_a11y_support_(false),
      thick_frame_(true),
#endif
      keyboard_event_handler_(new views::UnhandledKeyboardEventHandler),
      disable_count_(0),
      use_content_size_(false),
      movable_(true),
      resizable_(true),
      maximizable_(true),
      minimizable_(true),
      fullscreenable_(true) {
  options.Get(options::kTitle, &title_);
  options.Get(options::kAutoHideMenuBar, &menu_bar_autohide_);
#if defined(OS_WIN)