private Splitter getAssociatedSplitter(final Widget child) {
        // If a widget has a next sibling, it must be a splitter, because the only widget that *isn't* followed
        // by a splitter must be the CENTER, which has no associated splitter.
        final int idx = getWidgetIndex(child);
        if (idx > -1 && idx < getWidgetCount() - 1) {
            final Widget splitter = getWidget(idx + 1);
            assert splitter instanceof Splitter : "Expected child widget to be splitter";
            return (Splitter) splitter;
        }
        return null;
    }
Sets the minimum allowable size for the given widget.
<p>
<p>
Its associated splitter cannot be dragged to a position that would make
it smaller than this size. This method has no effect for the
{@link DockLayoutPanel.Direction#CENTER} widget.
</p>

@param child   the child whose minimum size will be set
@param minSize the minimum size for this widget
stroom-core-client-widget/src/main/java/com/google/gwt/user/client/ui/MySplitLayoutPanel.java