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

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

 
-class HTMLTableSectionElementJs extends HTMLElementJs implements HTMLTableSectionElement native "*HTMLTableSectionElement" {
+class _HTMLTableSectionElementJs extends _HTMLElementJs implements HTMLTableSectionElement native "*HTMLTableSectionElement" {
 
   String get align() native "return this.align;";
 
   void set align(String value) native "this.align = value;";
 
   String get ch() native "return this.ch;";
 
   void set ch(String value) native "this.ch = value;";
 
   String get chOff() native "return this.chOff;";
 
   void set chOff(String value) native "this.chOff = value;";
 
-  HTMLCollectionJs get rows() native "return this.rows;";
+  _HTMLCollectionJs get rows() native "return this.rows;";
 
   String get vAlign() native "return this.vAlign;";
 
   void set vAlign(String value) native "this.vAlign = value;";
 
   void deleteRow(int index) native;
 
-  HTMLElementJs insertRow(int index) native;
+  _HTMLElementJs insertRow(int index) native;
 }