anchor.diff:  
       _overrideNextRouteGist = null;
   
  +    _gistIdInProgress = gistId;
       gistLoader.loadGist(gistId).then((Gist gist) {
         _editableGist.setBackingGist(gist);
   
  
positive.code:       final message = 'Error loading gist $gistId.';
        showSnackbar(message);
        _logger.severe('$message: $e');
      });
    }
  
  
negative.code:   }
  
    void _showGist(String gistId) {
      if (_gistIdInProgress == gistId) {
        return;
      }
      // Don't auto-run if we're re-loading some unsaved edits; the gist might
      // have halting issues (#384).
      var loadedFromSaved = false;
  