Port DocumentFragment to the new wrapperless DOM.

client/dom/templates/html/interface/interface_DocumentFragment.darttemplate

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+interface DocumentFragment extends Element default _$(ID)FactoryProvider {
+
+  DocumentFragment();
+
+  DocumentFragment.html(String html);
+
+  // TODO(nweiz): enable these when XML and/or SVG are ported
+  // /** WARNING: Currently this doesn't work on Dartium (issue 649). */
+  // DocumentFragment.xml(String xml);
+  // DocumentFragment.svg(String svg);
+
+  DocumentFragment clone(bool deep);
+
+$!MEMBERS
+}