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

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

 
 class _MediaListJs extends _DOMTypeJs implements MediaList native "*MediaList" {
 
-  int get length() native "return this.length;";
+  final int length;
 
-  String get mediaText() native "return this.mediaText;";
-
-  void set mediaText(String value) native "this.mediaText = value;";
+  String mediaText;
 
   String operator[](int index) native "return this[index];";
 
   void operator[]=(int index, String value) {
     throw new UnsupportedOperationException("Cannot assign element of immutable List.");
   }
   // -- start List<String> mixins.
   // String is the element type.
 
   // From Iterable<String>:
@@ skipping 60 matching lines @@
       _Lists.getRange(this, start, length, <String>[]);
 
   // -- end List<String> mixins.
 
   void appendMedium(String newMedium) native;
 
   void deleteMedium(String oldMedium) native;
 
   String item(int index) native;
 }