function appendDrawCallGroup()
        {
            var index = self._drawCallGroupsCount || 0;
            var data = {};
            data[0] = "";
            data[1] = WebInspector.UIString("Draw call group #%d", index + 1);
            data[2] = "";
            var node = new WebInspector.DataGridNode(data);
            node.selectable = true;
            self._drawCallGroupsCount = index + 1;
            frameNode.appendChild(node);
            return node;
        }
@param {!WebInspector.DataGridNode} frameNode
@param {!Array.<!WebInspector.DataGridNode>} callNodes
@param {number} fromIndex
@param {number} toIndex not inclusive