Make dart:dom implementation types private so they don't muddle the docs.

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

 
-class CharacterDataJs extends NodeJs implements CharacterData native "*CharacterData" {
+class _CharacterDataJs extends _NodeJs implements CharacterData native "*CharacterData" {
 
   String get data() native "return this.data;";
 
   void set data(String value) native "this.data = value;";
 
   int get length() native "return this.length;";
 
   void appendData(String data) native;
 
   void deleteData(int offset, int length) native;
 
   void insertData(int offset, String data) native;
 
   void replaceData(int offset, int length, String data) native;
 
   String substringData(int offset, int length) native;
 }