rem: QSize MessageText::sizeHint() const { return QSize(contentsWidth(), contentsHeight() + horizontalScrollBar()->height()); }
add: virtual QSize sizeHint() const  { return QSize(contentsWidth(), contentsHeight() + scrollBarHeight()); }
context: QSize MessageText::sizeHint() const{	return QSize(contentsWidth(), contentsHeight() + horizontalScrollBar()->height());}