function createStepLine(parentElement, x, strokeColor)
        {
            var line = parentElement.createSVGChild("line");
            line.setAttribute("x1", x);
            line.setAttribute("x2", x);
            line.setAttribute("y1", WebInspector.AnimationUI.Options.AnimationMargin);
            line.setAttribute("y2", WebInspector.AnimationUI.Options.AnimationHeight);
            line.style.stroke = strokeColor;
        }
@param {!Element} parentElement
@param {number} x
@param {string} strokeColor