function styleSheetComparator(a, b)
        {
            if (a.sourceURL < b.sourceURL)
                return -1;
            else if (a.sourceURL > b.sourceURL)
                return 1;
            return a.startLine - b.startLine || a.startColumn - b.startColumn;
        }
@param {!WebInspector.CSSStyleSheetHeader} a
@param {!WebInspector.CSSStyleSheetHeader} b
@return {number}