private int getScrollBarHeight() {
        final int scrollBarWidth = ScrollbarMetrics.getHorizontalScrollBarWidth();

        int height = getOffsetHeight();
        height -= scrollBarWidth;
        // If we aren't using a chrome browser then there will be scroll bar
        // buttons that we need to remove.
        if (!isChrome()) {
            height -= (2 * scrollBarWidth);
        }
        return height;
    }
Redraws the overview bar. This is called when indicators are
added/removed, when indicators are set to be displayed and when the
widget is resized.
stroom-core-client-widget/src/main/java/stroom/editor/client/view/RightBar.java