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

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

 
 class _SVGRectJs extends _DOMTypeJs implements SVGRect native "*SVGRect" {
 
-  num get height() native "return this.height;";
+  num height;
 
-  void set height(num value) native "this.height = value;";
+  num width;
 
-  num get width() native "return this.width;";
+  num x;
 
-  void set width(num value) native "this.width = value;";
-
-  num get x() native "return this.x;";
-
-  void set x(num value) native "this.x = value;";
-
-  num get y() native "return this.y;";
-
-  void set y(num value) native "this.y = value;";
+  num y;
 }