* Electron version: 1.6.5
* Operating system: macOS Sierra

If you have a window with native tab bar to the top and you open a new window, it will open as separate window. But if you are in fullscreen mode, that new window will be attached as tab. Would it make sense to have API to force a window to open into an existing tab group or not? This would make it possible to give the user the choice of wether a window should open as tab or not independent from being in fullscreen mode or not.

Not even sure such API exists on macOS though.

/cc @tonyganch
atom/browser/native_window.h
virtual void MergeAllWindows();
  virtual void MoveTabToNewWindow();
  virtual void ToggleTabBar();
  
  virtual void FocusOnWebView();
  virtual void BlurWebView();
  virtual bool IsWebViewFocused();
  
  virtual void SetAutoHideMenuBar(bool auto_hide);
  virtual bool IsMenuBarAutoHide();
  virtual void SetMenuBarVisibility(bool visible);
  virtual bool IsMenuBarVisible();
  
  double GetAspectRatio();
  gfx::Size GetAspectRatioExtraSize();
  virtual void SetAspectRatio(double aspect_ratio, const gfx::Size& extra_size);
  
  virtual void PreviewFile(const std::string& path,
                           const std::string& display_name);
  virtual void CloseFilePreview();
  base::WeakPtr<NativeWindow> GetWeakPtr() {
    return weak_factory_.GetWeakPtr();
  }
  
  virtual void RequestToClosePage();
  
  virtual void CloseContents(content::WebContents* source);
  virtual void RendererUnresponsive(content::WebContents* source);
  virtual void RendererResponsive(content::WebContents* source);
  virtual void HandleKeyboardEvent(