anchor.diff:      session.useWorker = false;
     }
   
  -  ace.EditSession get currentSession => _aceEditor.session;
  +  ace.EditSession get currentSession => _currentSession;
   
     void switchTo(ace.EditSession session, [workspace.File file]) {
       if (_foldListenerSubscription != null) {
  
positive.code: 
    @override
    void deactivate() {
      super.deactivate();
      _markdown.deactivate();
    }
  
    @override
  
negative.code:   void _handleGotoLineViewClosed(_) => focus();
  
    void _scrollToBeginningOfDocument(_) {
      _currentSession.scrollTop = 0;
    }
  
    void _scrollToEndOfDocument(_) {
      int lineHeight = html.querySelector('.ace_gutter-cell').clientHeight;
      _currentSession.scrollTop = _currentSession.document.length * lineHeight;
    }
  
    NavigationLocation get navigationLocation {
      if (currentFile == null) return null;
      ace.Range range = _aceEditor.selection.range;
      int offsetStart = _currentSession.document.positionToIndex(range.start);
      int offsetEnd = _currentSession.document.positionToIndex(range.end);
      Span span = new Span(offsetStart, offsetEnd - offsetStart);
      return new NavigationLocation(currentFile, span);
    }
  