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

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

 
-class HTMLVideoElementJs extends HTMLMediaElementJs implements HTMLVideoElement native "*HTMLVideoElement" {
+class _HTMLVideoElementJs extends _HTMLMediaElementJs implements HTMLVideoElement native "*HTMLVideoElement" {
 
   int get height() native "return this.height;";
 
   void set height(int value) native "this.height = value;";
 
   String get poster() native "return this.poster;";
 
   void set poster(String value) native "this.poster = value;";
 
   int get videoHeight() native "return this.videoHeight;";
@@ skipping 13 matching lines @@
   void set width(int value) native "this.width = value;";
 
   void webkitEnterFullScreen() native;
 
   void webkitEnterFullscreen() native;
 
   void webkitExitFullScreen() native;
 
   void webkitExitFullscreen() native;
 }