public static Position getPosition(final PopupPosition popupPosition,
                                       final int offsetWidth,
                                       final int offsetHeight) {
        return getPosition(0, popupPosition, offsetWidth, offsetHeight);
    }
Positions the popup, called after the offset width and height of the
popup are known.
stroom-core-client-widget/src/main/java/stroom/widget/popup/client/presenter/PositionUtil.java