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

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

Index: client/dom/generated/src/frog/HTMLTrackElement.dart
diff --git a/client/dom/generated/src/frog/HTMLTrackElement.dart b/client/dom/generated/src/frog/HTMLTrackElement.dart
index 80671b78c5923a3fe6b3ab3a3b234c5cfaa8f15f..36a81462fd0e804f1cef7ce9cda34a5c6ffdfc79 100644
--- a/client/dom/generated/src/frog/HTMLTrackElement.dart
+++ b/client/dom/generated/src/frog/HTMLTrackElement.dart
@@ -9,27 +9,17 @@ class _HTMLTrackElementJs extends _HTMLElementJs implements HTMLTrackElement nat
 
   static final int NONE = 0;
 
-  bool get isDefault() native "return this.isDefault;";
+  bool isDefault;
 
-  void set isDefault(bool value) native "this.isDefault = value;";
+  String kind;
 
-  String get kind() native "return this.kind;";
+  String label;
 
-  void set kind(String value) native "this.kind = value;";
+  final int readyState;
 
-  String get label() native "return this.label;";
+  String src;
 
-  void set label(String value) native "this.label = value;";
+  String srclang;
 
-  int get readyState() native "return this.readyState;";
-
-  String get src() native "return this.src;";
-
-  void set src(String value) native "this.src = value;";
-
-  String get srclang() native "return this.srclang;";
-
-  void set srclang(String value) native "this.srclang = value;";
-
-  _TextTrackJs get track() native "return this.track;";
+  final _TextTrackJs track;
 }