feat(NativeWindowMac): addTabbedWindow

Add support for the [`NSWindow addTabbedWindow`][nsw] method on MacOSX

This plays nicely with the changes from #9052 and #9725

Usage samples available in [this commit][c] in my fork of
`electron-quick-start`

[nsw]: 1855947-addtabbedwindow
[c]: 79f06591df

atom/browser/native_window.h

@@ -190,6 +190,7 @@ class NativeWindow : public base::SupportsUserData,
   virtual void MergeAllWindows();
   virtual void MoveTabToNewWindow();
   virtual void ToggleTabBar();
+  virtual void AddTabbedWindow(NativeWindow* window);
 
   // Webview APIs.
   virtual void FocusOnWebView();