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

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

Index: client/dom/generated/src/frog/MutationEvent.dart
diff --git a/client/dom/generated/src/frog/MutationEvent.dart b/client/dom/generated/src/frog/MutationEvent.dart
index 9081de8e596365b322cdf42c3bb68821f6daf6ae..24c56f601d0e2087e68c3640411148cf74ab3605 100644
--- a/client/dom/generated/src/frog/MutationEvent.dart
+++ b/client/dom/generated/src/frog/MutationEvent.dart
@@ -1,5 +1,5 @@
 
-class MutationEventJs extends EventJs implements MutationEvent native "*MutationEvent" {
+class _MutationEventJs extends _EventJs implements MutationEvent native "*MutationEvent" {
 
   static final int ADDITION = 2;
 
@@ -15,7 +15,7 @@ class MutationEventJs extends EventJs implements MutationEvent native "*Mutation
 
   String get prevValue() native "return this.prevValue;";
 
-  NodeJs get relatedNode() native "return this.relatedNode;";
+  _NodeJs get relatedNode() native "return this.relatedNode;";
 
-  void initMutationEvent(String type, bool canBubble, bool cancelable, NodeJs relatedNode, String prevValue, String newValue, String attrName, int attrChange) native;
+  void initMutationEvent(String type, bool canBubble, bool cancelable, _NodeJs relatedNode, String prevValue, String newValue, String attrName, int attrChange) native;
 }