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### Preflight Checklist
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* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  * <!-- (output of `node_modules/.bin/electron --version`) e.g. 4.0.3 --> 4.1.4
* **Operating System:** 
  * <!-- (Platform and Version) e.g. macOS 10.13.6 / Windows 10 (1803) / Ubuntu 18.04 x64 -->macOS
* **Last Known Working Electron version:**:
  * <!-- (if applicable) e.g. 3.1.0 --> Never

### Expected Behavior
When `titleBarStyle` is set to `customButtonsOnHover`, the semaphore buttons *should not* appear on hover if the `maximizable` and `minimizable` options are set to `false`.

### Actual Behavior
When `titleBarStyle` is set to `customButtonsOnHover`, the semaphore buttons appear on hover regardless if the `maximizable` and `minimizable` options are set to `false`.

### To Reproduce
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### Screenshots
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### Additional Information
The reason for this issue is to be able to get rid of the gray line at the top of the `BrowserWindow` described here https://github.com/electron/electron/issues/18364

atom/browser/native_window_mac.h
bool is_kiosk_ = false;
  bool was_fullscreen_ = false;
  bool zoom_to_page_width_ = false;
  bool fullscreen_window_title_ = false;
  bool resizable_ = true;
  NSInteger attention_request_id_ = 0;  
  
  NSApplicationPresentationOptions kiosk_options_;
  
  TitleBarStyle title_bar_style_ = TitleBarStyle::NORMAL;
  
  
  base::Optional<bool> window_button_visibility_;
  
  bool always_simple_fullscreen_ = false;
  bool is_simple_fullscreen_ = false;
  bool was_maximizable_ = false;
  bool was_movable_ = false;
  NSRect original_frame_;
  NSInteger original_level_;
  NSUInteger simple_fullscreen_mask_;
  base::scoped_nsobject<NSColor> background_color_before_vibrancy_;
  bool transparency_before_vibrancy_ = false;
  
  NSApplicationPresentationOptions simple_fullscreen_options_;
  DISALLOW_COPY_AND_ASSIGN(NativeWindowMac);
};
}  
#endif