Reapply revision 11570, custom callbacks are now implemented in dartium.

lib/html/doc/interface/DOMFormData.dartdoc

Index: lib/html/doc/interface/DOMFormData.dartdoc
diff --git a/lib/html/doc/interface/DOMFormData.dartdoc b/lib/html/doc/interface/DOMFormData.dartdoc
deleted file mode 100644
index 1f2ea61b176574435318ad3de1ac2935bb491a76..0000000000000000000000000000000000000000
--- a/lib/html/doc/interface/DOMFormData.dartdoc
+++ /dev/null
@@ -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);
-}