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

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

 
-class HTMLCollectionJs extends DOMTypeJs implements HTMLCollection native "*HTMLCollection" {
+class _HTMLCollectionJs extends _DOMTypeJs implements HTMLCollection native "*HTMLCollection" {
 
   int get length() native "return this.length;";
 
-  NodeJs operator[](int index) native "return this[index];";
+  _NodeJs operator[](int index) native "return this[index];";
 
-  void operator[]=(int index, NodeJs value) {
+  void operator[]=(int index, _NodeJs value) {
     throw new UnsupportedOperationException("Cannot assign element of immutable List.");
   }
   // -- start List<Node> mixins.
   // Node is the element type.
 
   // From Iterable<Node>:
 
   Iterator<Node> iterator() {
     // Note: NodeLists are not fixed size. And most probably length shouldn't
     // be cached in both iterator _and_ forEach method. For now caching it
@@ skipping 50 matching lines @@
     throw new UnsupportedOperationException("Cannot removeRange on immutable List.");
   }
   void insertRange(int start, int length, [Node initialValue]) {
     throw new UnsupportedOperationException("Cannot insertRange on immutable List.");
   }
   List<Node> getRange(int start, int length) =>
       _Lists.getRange(this, start, length, <Node>[]);
 
   // -- end List<Node> mixins.
 
-  NodeJs item(int index) native;
+  _NodeJs item(int index) native;
 
-  NodeJs namedItem(String name) native;
+  _NodeJs namedItem(String name) native;
 }