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

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

 
-class OperationNotAllowedExceptionJs extends DOMTypeJs implements OperationNotAllowedException native "*OperationNotAllowedException" {
+class _OperationNotAllowedExceptionJs extends _DOMTypeJs implements OperationNotAllowedException native "*OperationNotAllowedException" {
 
   static final int NOT_ALLOWED_ERR = 1;
 
   int get code() native "return this.code;";
 
   String get message() native "return this.message;";
 
   String get name() native "return this.name;";
 
   String toString() native;
 }