Move frog dart:dom from fields to getters/setters.

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

 
 class NodeList native "*NodeList" {
 
-  int length;
+  int get length() native "return this.length;";
 
   Node operator[](int index) native;
 
   void operator[]=(int index, Node value) {
     throw new UnsupportedOperationException("Cannot assign element of immutable List.");
   }
 
   Node item(int index) native;
 
   var dartObjectLocalStorage;
 
   String get typeName() native;
 }