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

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

 
 class _HTMLBaseElementJs extends _HTMLElementJs implements HTMLBaseElement native "*HTMLBaseElement" {
 
-  String get href() native "return this.href;";
+  String href;
 
-  void set href(String value) native "this.href = value;";
-
-  String get target() native "return this.target;";
-
-  void set target(String value) native "this.target = value;";
+  String target;
 }