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

lib/html/dart2js/html_dart2js.dart

Index: lib/html/dart2js/html_dart2js.dart
===================================================================
--- lib/html/dart2js/html_dart2js.dart	(revision 11420)
+++ lib/html/dart2js/html_dart2js.dart	(working copy)
@@ -4352,11 +4352,6 @@
   final _DirectoryEntrySyncImpl root;
 }
 
-class _DOMFormDataImpl implements DOMFormData native "*DOMFormData" {
-
-  void append(String name, String value, String filename) native;
-}
-
 class _DOMImplementationImpl implements DOMImplementation native "*DOMImplementation" {
 
   _CSSStyleSheetImpl createCSSStyleSheet(String title, String media) native;
@@ -7312,6 +7307,11 @@
   String size;
 }
 
+class _FormDataImpl implements FormData native "*FormData" {
+
+  void append(String name, String value, String filename) native;
+}
+
 class _FormElementImpl extends _ElementImpl implements FormElement native "*HTMLFormElement" {
 
   String acceptCharset;
@@ -18068,6 +18068,11 @@
     return _e;
   }
 
+  factory FormElement() {
+    _FormElementImpl _e = _document.$dom_createElement("form");
+    return _e;
+  }
+
   factory HRElement() {
     _HRElementImpl _e = _document.$dom_createElement("hr");
     return _e;
@@ -18310,6 +18315,16 @@
 // 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 = null]) native '''
+    if (form == null) return new FormData();
+    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 _HttpRequestFactoryProvider {
   factory HttpRequest() native 'return new XMLHttpRequest();';
 
@@ -22759,18 +22774,6 @@
 
 // WARNING: Do not edit - generated code.
 
-/// @domName DOMFormData
-interface DOMFormData {
-
-  /** @domName DOMFormData.append */
-  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.
-
 /// @domName DOMImplementation
 interface DOMImplementation {
 
@@ -25102,9 +25105,25 @@
 
 // WARNING: Do not edit - generated code.
 
+/// @domName FormData
+interface FormData default _FormDataFactoryProvider {
+
+  FormData([FormElement form]);
+
+  /** @domName FormData.append */
+  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.
+
 /// @domName HTMLFormElement
-interface FormElement extends Element {
+interface FormElement extends Element default _Elements {
 
+  FormElement();
+
   /** @domName HTMLFormElement.acceptCharset */
   String acceptCharset;