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

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

 
 class _CSSRuleJs extends _DOMTypeJs implements CSSRule native "*CSSRule" {
 
   static final int CHARSET_RULE = 2;
 
   static final int FONT_FACE_RULE = 5;
 
   static final int IMPORT_RULE = 3;
 
   static final int MEDIA_RULE = 4;
 
   static final int PAGE_RULE = 6;
 
   static final int STYLE_RULE = 1;
 
   static final int UNKNOWN_RULE = 0;
 
   static final int WEBKIT_KEYFRAMES_RULE = 8;
 
   static final int WEBKIT_KEYFRAME_RULE = 9;
 
   static final int WEBKIT_REGION_RULE = 10;
 
-  String get cssText() native "return this.cssText;";
+  String cssText;
 
-  void set cssText(String value) native "this.cssText = value;";
+  final _CSSRuleJs parentRule;
 
-  _CSSRuleJs get parentRule() native "return this.parentRule;";
+  final _CSSStyleSheetJs parentStyleSheet;
 
-  _CSSStyleSheetJs get parentStyleSheet() native "return this.parentStyleSheet;";
-
-  int get type() native "return this.type;";
+  final int type;
 }