anchor.diff:    Rect _renderedViewport;
     Rect _viewport = Rect.zero;
   
  -
     void _dispatchMouseMoveEvent() {
       if (_onMouseMove != null) {
         _onMouseMove(_clientToGlobal(_currentMouseHover));
  
positive.code: import 'dart:html';
  import 'dart:js';
  
  import 'package:meta/meta.dart';
  
negative.code: 
    _ChunkPosition get position => _position;
    _ChunkPosition _position;
  
    set position(_ChunkPosition p) {
      if (_position == p) return;
      _position = p;
  