Use fields in hidden native DOM classes instead of getters/setters.

client/dom/generated/src/frog/SVGMPathElement.dart

 
 class _SVGMPathElementJs extends _SVGElementJs implements SVGMPathElement native "*SVGMPathElement" {
 
   // From SVGURIReference
 
-  _SVGAnimatedStringJs get href() native "return this.href;";
+  final _SVGAnimatedStringJs href;
 
   // From SVGExternalResourcesRequired
 
-  _SVGAnimatedBooleanJs get externalResourcesRequired() native "return this.externalResourcesRequired;";
+  final _SVGAnimatedBooleanJs externalResourcesRequired;
 }