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

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

Index: client/dom/generated/src/frog/ElementTraversal.dart
diff --git a/client/dom/generated/src/frog/ElementTraversal.dart b/client/dom/generated/src/frog/ElementTraversal.dart
index 0c8cc30bcd27a52fd0295a8124e4c1aef1a9fdde..d930fcca5dd17b73644829635e20f05d75b931d3 100644
--- a/client/dom/generated/src/frog/ElementTraversal.dart
+++ b/client/dom/generated/src/frog/ElementTraversal.dart
@@ -1,13 +1,13 @@
 
-class ElementTraversalJs extends DOMTypeJs implements ElementTraversal native "*ElementTraversal" {
+class _ElementTraversalJs extends _DOMTypeJs implements ElementTraversal native "*ElementTraversal" {
 
   int get childElementCount() native "return this.childElementCount;";
 
-  ElementJs get firstElementChild() native "return this.firstElementChild;";
+  _ElementJs get firstElementChild() native "return this.firstElementChild;";
 
-  ElementJs get lastElementChild() native "return this.lastElementChild;";
+  _ElementJs get lastElementChild() native "return this.lastElementChild;";
 
-  ElementJs get nextElementSibling() native "return this.nextElementSibling;";
+  _ElementJs get nextElementSibling() native "return this.nextElementSibling;";
 
-  ElementJs get previousElementSibling() native "return this.previousElementSibling;";
+  _ElementJs get previousElementSibling() native "return this.previousElementSibling;";
 }