DetailsWidget: make cacheBackground public

Change-Id: Ib3725298f77f8ea878717e31bffceffc8bf1f7c6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/libs/utils/detailswidget.h

@@ -86,6 +86,8 @@ public:
     /// Sets an icon, only supported if useCheckBox is true
     void setIcon(const QIcon &icon);
 
+    static QPixmap createBackground(const QSize &size, int topHeight, QWidget *widget);
+
 signals:
     void checked(bool);
     void linkActivated(const QString &link);