code: function isExclusiveToPane(file, paneId) {
          paneId = paneId === ACTIVE_PANE && _activePaneId ? _activePaneId : paneId;
          var index = _.findIndex(_mruList, function (record) {
              return (record.file.fullPath === file.fullPath && record.paneId !== paneId);
          });
          return index === -1;
      }
docs: Checks whether a file is listed exclusively in the provided pane
  @param {!File} File - the file
  @return {{file:File, paneId:string}}