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

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

Index: client/dom/generated/src/frog/Rect.dart
diff --git a/client/dom/generated/src/frog/Rect.dart b/client/dom/generated/src/frog/Rect.dart
index 97e7ecb431f53f45b240e9989411a3a7ffb4307d..065d950e4a141de5549163e215e24302631ea540 100644
--- a/client/dom/generated/src/frog/Rect.dart
+++ b/client/dom/generated/src/frog/Rect.dart
@@ -1,11 +1,11 @@
 
 class _RectJs extends _DOMTypeJs implements Rect native "*Rect" {
 
-  _CSSPrimitiveValueJs get bottom() native "return this.bottom;";
+  final _CSSPrimitiveValueJs bottom;
 
-  _CSSPrimitiveValueJs get left() native "return this.left;";
+  final _CSSPrimitiveValueJs left;
 
-  _CSSPrimitiveValueJs get right() native "return this.right;";
+  final _CSSPrimitiveValueJs right;
 
-  _CSSPrimitiveValueJs get top() native "return this.top;";
+  final _CSSPrimitiveValueJs top;
 }