code: function getWorkingSet(paneId) {
          var result = [];
  
          _forEachPaneOrPanes(paneId, function (pane) {
              var viewList = pane.getViewList();
              result = _.union(result, viewList);
          });
  
          return result;
      }
docs: Retrieves the WorkingSet for the given paneId not including temporary views
  @param {!string} paneId - id of the pane in which to get the view list, ALL_PANES or ACTIVE_PANE
  @return {Array.<File>}