code: function _isOpenAndDirty(file) {
          // working set item might never have been opened; if so, then it's definitely not dirty
          var docIfOpen = DocumentManager.getOpenDocumentForPath(file.fullPath);
          return (docIfOpen && docIfOpen.isDirty);
      }
docs: Determines if a file is dirty
  @private
  @param {!File} file - file to test
  @return {boolean} true if the file is dirty, false otherwise