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

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

Index: client/dom/generated/src/frog/ValidityState.dart
diff --git a/client/dom/generated/src/frog/ValidityState.dart b/client/dom/generated/src/frog/ValidityState.dart
index 68328c4ce32d513e0da9975414d0d9cee6e1acdf..92320dd70b90c0bb2e2ec8d32b7778e5dde62b46 100644
--- a/client/dom/generated/src/frog/ValidityState.dart
+++ b/client/dom/generated/src/frog/ValidityState.dart
@@ -1,21 +1,21 @@
 
 class _ValidityStateJs extends _DOMTypeJs implements ValidityState native "*ValidityState" {
 
-  bool get customError() native "return this.customError;";
+  final bool customError;
 
-  bool get patternMismatch() native "return this.patternMismatch;";
+  final bool patternMismatch;
 
-  bool get rangeOverflow() native "return this.rangeOverflow;";
+  final bool rangeOverflow;
 
-  bool get rangeUnderflow() native "return this.rangeUnderflow;";
+  final bool rangeUnderflow;
 
-  bool get stepMismatch() native "return this.stepMismatch;";
+  final bool stepMismatch;
 
-  bool get tooLong() native "return this.tooLong;";
+  final bool tooLong;
 
-  bool get typeMismatch() native "return this.typeMismatch;";
+  final bool typeMismatch;
 
-  bool get valid() native "return this.valid;";
+  final bool valid;
 
-  bool get valueMissing() native "return this.valueMissing;";
+  final bool valueMissing;
 }