* Electron version: 1.7.6
* Operating system: MacOS High Sierra GM

### Expected behavior

Title bar should not be invisible

![screen shot 2017-09-14 at 11 22 04 am](https://user-images.githubusercontent.com/320654/30441406-f34fe61a-993e-11e7-8592-244e50a92bb9.png)

### Actual behavior

Title bar is invisible

### How to reproduce
```
  mainWindow = new BrowserWindow({
      vibrancy: 'light',
      titleBarStyle: 'hiddenInset',
      width: 800,
      height: 600
  })
```

```
 $ git clone git@github.com:gerges/electron-quick-start.git -b  issue/invisible-titlebar
 $ npm install
 $ npm run start
```

atom/browser/native_window_mac.h
@class AtomNSWindowDelegate;
@class FullSizeContentView;
namespace atom {
class NativeWindowMac : public NativeWindow,
                        public content::RenderWidgetHost::InputEventObserver {
 public:
  NativeWindowMac(brightray::InspectableWebContents* inspectable_web_contents,
                  const mate::Dictionary& options,
                  NativeWindow* parent);
  ~NativeWindowMac() override;
  
  void Close() override;
  void CloseImmediately() override;
  void Focus(bool focus) override;
  bool IsFocused() override;
  void Show() override;
  void ShowInactive() override;
  void Hide() override;
  bool IsVisible() override;
  bool IsEnabled() override;
  void SetEnabled(bool enable) override;
  void Maximize() override;
  void Unmaximize() override;
  bool IsMaximized() override;
  void Minimize() override;