QHeaderViewPrivate::_q_layoutChanged() was not called when used in a
QTreeView because it was explicitly disconnected in setModel().
The disconnect was added sometime prio to Qt 4.3, but there the signal
was connected to the doItemsLayout() slot. This was correct since
QTreeView::doItemsLayout() is calling header->doItemsLayout().
In Qt 4.3.0 _q_layoutChanged() was introduced and the disconnect was
adjusted. But since _q_layoutChanged() is doing much more than
doItemsLayout() (e.g. restoring hidden sections), functionality was
lost. The problem was already observed for Qt 4.6 (QTBUG-18196) but
only partially fixed.
Task-number: QTBUG-41124
Task-number: QTBUG-54610
Change-Id: Id13a9930d0163812e12a0287016bab9c3aa02068
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
93dabeba9d