anchor.diff:    void setMarkers(List<workspace.Marker> markers) {
       List<ace.Annotation> annotations = [];
   
  -    int numberLines = currentSession.document.length;
  +    int numberLines = currentSession.screenLength;
       _recreateMiniMap();
   
       for (workspace.Marker marker in markers) {
  
positive.code:           type: annotationType);
        annotations.add(annotation);
  
        // TODO(ericarnold): This won't work with code folding.  Fix
        double markerHeightPercentage =
            marker.lineNum / numberLines * 100;
  
        html.Element minimapMarker = new html.Element.div();
        minimapMarker.classes.add("minimap-marker error");
  
negative.code:       if (_markerSubscription == null) {
          _markerSubscription = file.workspace.onMarkerChange.listen(
              _handleMarkerChange);
          currentSession.onChange.listen(
              (_) => setMarkers(currentFile.getMarkers()));
        }
      }
    }
  