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

lib/dom/dart2js/dom_dart2js.dart

Index: lib/dom/dart2js/dom_dart2js.dart
===================================================================
--- lib/dom/dart2js/dom_dart2js.dart	(revision 11420)
+++ lib/dom/dart2js/dom_dart2js.dart	(working copy)
@@ -1011,11 +1011,6 @@
   final _DirectoryEntrySyncJs root;
 }
 
-class _DOMFormDataJs extends _DOMTypeJs implements DOMFormData native "*DOMFormData" {
-
-  void append(String name, String value, String filename) native;
-}
-
 class _DOMImplementationJs extends _DOMTypeJs implements DOMImplementation native "*DOMImplementation" {
 
   _CSSStyleSheetJs createCSSStyleSheet(String title, String media) native;
@@ -2587,6 +2582,11 @@
   _Float64ArrayJs subarray(int start, [int end]) native;
 }
 
+class _FormDataJs extends _DOMTypeJs implements FormData native "*FormData" {
+
+  void append(String name, String value, String filename) native;
+}
+
 class _GamepadJs extends _DOMTypeJs implements Gamepad native "*Gamepad" {
 
   final List<num> axes;
@@ -12112,6 +12112,14 @@
 // 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 _FormDataFactoryProvider {
+  factory FormData([FormElement form]) native
+      '''return new FormData(form);''';
+}
+// 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 _HTMLAudioElementFactoryProvider {
   factory HTMLAudioElement([String src = null]) native
 '''
@@ -13623,19 +13631,6 @@
 
 // WARNING: Do not edit - generated code.
 
-interface FormData {
-
-  void append(String name, String value, String filename);
-}
-
-interface DOMFormData extends FormData {
-}
-// 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: Do not edit - generated code.
-
 interface DOMImplementation {
 
   CSSStyleSheet createCSSStyleSheet(String title, String media);
@@ -15254,6 +15249,18 @@
 
 // WARNING: Do not edit - generated code.
 
+interface FormData default _FormDataFactoryProvider {
+
+  FormData([FormElement form]);
+
+  void append(String name, String value, String filename);
+}
+// 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: Do not edit - generated code.
+
 interface Gamepad {
 
   final List<num> axes;