Provide a constructor for (DOM)FormData, and rename to the more standard name,

lib/html/doc/interface/DOMFormData.dartdoc

Index: lib/html/doc/interface/DOMFormData.dartdoc
===================================================================
--- lib/html/doc/interface/DOMFormData.dartdoc	(revision 11420)
+++ lib/html/doc/interface/DOMFormData.dartdoc	(working copy)
@@ -1,14 +0,0 @@
-// 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.
-
-// WARNING:
-//   This file contains documentation that is merged into the real source.
-//   Do not make code changes here.
-
-/// @domName DOMFormData
-interface DOMFormData {
-
-  /** @domName DOMFormData.append */
-  void append(String name, String value, String filename);
-}