QLayoutStyleInfo requires a widget to init the style from:
m_styleOption.initFrom(widget);

From QGraphicsLinearLayoutPrivate::styleInfo() and QGraphicsGridLayout::styleInfo() we are creating a pointer to a QWidget like:
static QWidget *wid = 0;
if (!wid)
wid = new QWidget;

and then passing it to:
return QLayoutStyleInfo(style, wid);

But that creates a leak. It will be nice to review the QLayoutStyleInfo to update this part of the code. QLayoutStyleInfo is only used in graphics view.