code: function addDerivedInfoForFile(fileCoverage) {
      var statementMap = fileCoverage.statementMap,
        statements = fileCoverage.s,
        lineMap;
  
      if (!fileCoverage.l) {
        fileCoverage.l = lineMap = {};
        Object.keys(statements).forEach(function (st) {
          var line = statementMap[st].start.line,
            count = statements[st],
            prevVal = lineMap[line];
          if (count === 0 && statementMap[st].skip) { count = 1; }
          if (typeof prevVal === 'undefined' || prevVal < count) {
            lineMap[line] = count;
          }
        });
      }
    }
docs: adds line coverage information to a file coverage object, reverse-engineering
  it from statement coverage. The object passed in is updated in place.
  
  Note that if line coverage information is already present in the object,
  it is not recomputed.
  
  @method addDerivedInfoForFile
  @static
  @param {Object} fileCoverage the coverage object for a single file