public void setWidgetMinSize(final Widget child, final int minSize) {
        assertIsChild(child);
        final Splitter splitter = getAssociatedSplitter(child);
        // The splitter is null for the center element.
        if (splitter != null) {
            splitter.setMinSize(minSize);
        }
    }
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 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/ThinSplitLayoutPanel.java