QtMacExtras's QMacNativeToolBar doesn't provide a way to add an NSView-based toolbar item

In Qt 4, I could create a toolbar with Mac-style "unified" appearance, then use setStyleSheet() to further customize the appearance of toolbar items. For example, see the attached image — I added 3 actions with custom styles to create the "Zoom" part of the toolbar.

In Qt 5, I tried using QtMacExtras::setNativeToolBar(), but my styles are ignored (which makes sense since it's rendering using a Cocoa widget instead of Qt code).

It would be great if there were a way to add an NSView to a QMacNativeToolBar.

I've attached the beginnings of a patch. It makes QMacToolButton public, and adds the constructor QMacToolButton::QMacToolButton(NSView *view, QAction *action) and other infrastructure... But it isn't quite working yet.