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