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

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

Index: client/dom/generated/src/frog/TextTrackList.dart
diff --git a/client/dom/generated/src/frog/TextTrackList.dart b/client/dom/generated/src/frog/TextTrackList.dart
index 348804a3036a66948228827e010e255161fa5ee7..4a7dc9584e4673b14d4a4a8e1f508267201f019e 100644
--- a/client/dom/generated/src/frog/TextTrackList.dart
+++ b/client/dom/generated/src/frog/TextTrackList.dart
@@ -1,5 +1,5 @@
 
-class TextTrackListJs extends DOMTypeJs implements TextTrackList native "*TextTrackList" {
+class _TextTrackListJs extends _DOMTypeJs implements TextTrackList native "*TextTrackList" {
 
   int get length() native "return this.length;";
 
@@ -9,9 +9,9 @@ class TextTrackListJs extends DOMTypeJs implements TextTrackList native "*TextTr
 
   void addEventListener(String type, EventListener listener, [bool useCapture = null]) native;
 
-  bool dispatchEvent(EventJs evt) native;
+  bool dispatchEvent(_EventJs evt) native;
 
-  TextTrackJs item(int index) native;
+  _TextTrackJs item(int index) native;
 
   void removeEventListener(String type, EventListener listener, [bool useCapture = null]) native;
 }