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

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

 
-class HTMLBaseFontElementJs extends HTMLElementJs implements HTMLBaseFontElement native "*HTMLBaseFontElement" {
+class _HTMLBaseFontElementJs extends _HTMLElementJs implements HTMLBaseFontElement native "*HTMLBaseFontElement" {
 
   String get color() native "return this.color;";
 
   void set color(String value) native "this.color = value;";
 
   String get face() native "return this.face;";
 
   void set face(String value) native "this.face = value;";
 
   int get size() native "return this.size;";
 
   void set size(int value) native "this.size = value;";
 }