Suggestion: Make QTreeViewPrivate::updateScrollBars() available as a protected function in QTreeView.

Scenario: When reimplementing QTreeView::updateGeometries() to support more widgets than one header element. The new updateGeometries() places all widgets on the right place and also does the "setViewportMargins()". It's not possible to call the QTreeViewPrivate::updateScrollBars() from there, so the scrollbars always fail to update unless the model inserts rows or the window resizes.

This would be fixed if QTreeViewPrivate::updateScrollBars()