Port DocumentFragment to the new wrapperless DOM.

client/html/html_dartium.dart

Index: client/html/html_dartium.dart
diff --git a/client/html/html_dartium.dart b/client/html/html_dartium.dart
index c5ef7a04de88ee4c835b99e36b6bfcebaf1d140e..74dfacc353f111da7a2b324c09f5fa7faccae105 100644
--- a/client/html/html_dartium.dart
+++ b/client/html/html_dartium.dart
@@ -1106,6 +1106,8 @@ _wrap(raw) {
       throw 'A document should never be wrapped directly. TODO(jacobr) XXX';
     case 'HTMLHtmlElement':
       return new _DocumentImpl._wrap(domObject);
+    case 'HTMLElement':
+      return new _UnknownElementImpl._wrap(domObject);
     case "EventTarget": return new _EventTargetImpl._wrap(domObject);
     case "AbstractWorker": return new _AbstractWorkerImpl._wrap(domObject);
     case "Node": return new _NodeImpl._wrap(domObject);