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

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

Index: client/dom/generated/src/frog/Screen.dart
diff --git a/client/dom/generated/src/frog/Screen.dart b/client/dom/generated/src/frog/Screen.dart
index ef7a73a425791768577093ec35f8330970f16bf5..cbbd2f201d7f060b93d948e71dc837b328e3badc 100644
--- a/client/dom/generated/src/frog/Screen.dart
+++ b/client/dom/generated/src/frog/Screen.dart
@@ -1,19 +1,19 @@
 
 class _ScreenJs extends _DOMTypeJs implements Screen native "*Screen" {
 
-  int get availHeight() native "return this.availHeight;";
+  final int availHeight;
 
-  int get availLeft() native "return this.availLeft;";
+  final int availLeft;
 
-  int get availTop() native "return this.availTop;";
+  final int availTop;
 
-  int get availWidth() native "return this.availWidth;";
+  final int availWidth;
 
-  int get colorDepth() native "return this.colorDepth;";
+  final int colorDepth;
 
-  int get height() native "return this.height;";
+  final int height;
 
-  int get pixelDepth() native "return this.pixelDepth;";
+  final int pixelDepth;
 
-  int get width() native "return this.width;";
+  final int width;
 }