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

lib/dom/templates/html/dart2js/factoryprovider_FormData.darttemplate

Index: lib/dom/templates/html/dart2js/factoryprovider_FormData.darttemplate
===================================================================
--- lib/dom/templates/html/dart2js/factoryprovider_FormData.darttemplate	(revision 0)
+++ lib/dom/templates/html/dart2js/factoryprovider_FormData.darttemplate	(revision 0)
@@ -0,0 +1,10 @@
+// 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.
+
+class $FACTORYPROVIDER {
+  factory FormData([FormElement form = null]) native '''
+    if (form == null) return new FormData();
+    return new FormData(form);
+  ''';
+}