anchor.diff:  
     // private methods that modify map state
   
  -  _resetView(center, zoom, preserveMapOffset, afterZoomAnim) {
  +  _resetView(center, zoom, [preserveMapOffset=false, afterZoomAnim=false]) {
   
       var zoomChanged = (this._zoom != zoom);
   
  
positive.code:     var container = this._container;
  
      L.DomUtil.addClass(container, 'leaflet-container' +
        (L.Browser.touch ? ' leaflet-touch' : '') +
        (L.Browser.retina ? ' leaflet-retina' : '') +
        (L.Browser.ielt9 ? ' leaflet-oldie' : '') +
        (this.options.fadeAnimation ? ' leaflet-fade-anim' : ''));
  
      var position = L.DomUtil.getStyle(container, 'position');
  
      if (position != 'absolute' && position != 'relative' && position != 'fixed') {
        container.style.position = 'relative';
  
negative.code: import 'dart:html';
  import 'dart:math' as math;
  
  class BaseMap {
    Map<String, Object> options = {
      'crs': crs.EPSG3857,
      'fadeAnimation': DomUtil.TRANSITION && !Browser.android23,
      'trackResize': true,
      'markerZoomAnimation': DomUtil.TRANSITION && Browser.any3d
    };
  
    List _handlers;
  
  