private double getWidthOrHeightOfNode(final TreeNode treeNode, final boolean returnWidth) {
        return returnWidth
                ? getNodeWidth(treeNode)
                : getNodeHeight(treeNode);
    }
Returns the {@link NodeExtentProvider} used by this
{@link AbegoTreeLayout}.
stroom-core-client-widget/src/main/java/stroom/widget/htree/client/treelayout/AbegoTreeLayout.java