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

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

 
-class HTMLMetaElementJs extends HTMLElementJs implements HTMLMetaElement native "*HTMLMetaElement" {
+class _HTMLMetaElementJs extends _HTMLElementJs implements HTMLMetaElement native "*HTMLMetaElement" {
 
   String get content() native "return this.content;";
 
   void set content(String value) native "this.content = value;";
 
   String get httpEquiv() native "return this.httpEquiv;";
 
   void set httpEquiv(String value) native "this.httpEquiv = value;";
 
   String get name() native "return this.name;";
 
   void set name(String value) native "this.name = value;";
 
   String get scheme() native "return this.scheme;";
 
   void set scheme(String value) native "this.scheme = value;";
 }