* 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
std::string* error = nullptr) = 0;
  virtual bool IsAlwaysOnTop() = 0;
  virtual void Center() = 0;
  virtual void Invalidate() = 0;
  virtual void SetTitle(const std::string& title) = 0;
  virtual std::string GetTitle() = 0;
  virtual void FlashFrame(bool flash) = 0;
  virtual void SetSkipTaskbar(bool skip) = 0;
  virtual void SetSimpleFullScreen(bool simple_fullscreen) = 0;
  virtual bool IsSimpleFullScreen() = 0;
  virtual void SetKiosk(bool kiosk) = 0;
  virtual bool IsKiosk() = 0;
  virtual void SetBackgroundColor(const std::string& color_name) = 0;
  virtual void SetHasShadow(bool has_shadow) = 0;
  virtual bool HasShadow() = 0;
  virtual void SetRepresentedFilename(const std::string& filename);
  virtual std::string GetRepresentedFilename();
  virtual void SetDocumentEdited(bool edited);
  virtual bool IsDocumentEdited();
  virtual void SetIgnoreMouseEvents(bool ignore, bool forward) = 0;
  virtual void SetContentProtection(bool enable) = 0;
  virtual void SetFocusable(bool focusable);
  virtual void SetMenu(AtomMenuModel* menu);
  virtual void SetParentWindow(NativeWindow* parent);
  virtual void SetBrowserView(NativeBrowserView* browser_view) = 0;
  virtual gfx::NativeView GetNativeView() const = 0;
  virtual gfx::NativeWindow GetNativeWindow() const = 0;
  virtual gfx::AcceleratedWidget GetAcceleratedWidget() const = 0;
  
  enum ProgressState {