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

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

 
-class HTMLStyleElementJs extends HTMLElementJs implements HTMLStyleElement native "*HTMLStyleElement" {
+class _HTMLStyleElementJs extends _HTMLElementJs implements HTMLStyleElement native "*HTMLStyleElement" {
 
   bool get disabled() native "return this.disabled;";
 
   void set disabled(bool value) native "this.disabled = value;";
 
   String get media() native "return this.media;";
 
   void set media(String value) native "this.media = value;";
 
   bool get scoped() native "return this.scoped;";
 
   void set scoped(bool value) native "this.scoped = value;";
 
-  StyleSheetJs get sheet() native "return this.sheet;";
+  _StyleSheetJs get sheet() native "return this.sheet;";
 
   String get type() native "return this.type;";
 
   void set type(String value) native "this.type = value;";
 }