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

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

 
-class HTMLAppletElementJs extends HTMLElementJs implements HTMLAppletElement native "*HTMLAppletElement" {
+class _HTMLAppletElementJs extends _HTMLElementJs implements HTMLAppletElement native "*HTMLAppletElement" {
 
   String get align() native "return this.align;";
 
   void set align(String value) native "this.align = value;";
 
   String get alt() native "return this.alt;";
 
   void set alt(String value) native "this.alt = value;";
 
   String get archive() native "return this.archive;";
@@ skipping 25 matching lines @@
   void set object(String value) native "this.object = value;";
 
   String get vspace() native "return this.vspace;";
 
   void set vspace(String value) native "this.vspace = value;";
 
   String get width() native "return this.width;";
 
   void set width(String value) native "this.width = value;";
 }