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

lib/dom/src/dart2js_FactoryProviders.dart

Index: lib/dom/src/dart2js_FactoryProviders.dart
diff --git a/lib/dom/src/dart2js_FactoryProviders.dart b/lib/dom/src/dart2js_FactoryProviders.dart
index de90d8522b53ac343f075bab77332d7855ce7716..6f68f1b3b50d7efc8dd09fd0fea01c8c5573e2f0 100644
--- a/lib/dom/src/dart2js_FactoryProviders.dart
+++ b/lib/dom/src/dart2js_FactoryProviders.dart
@@ -10,6 +10,15 @@ class _AudioContextFactoryProvider {
 ''';
 }
 
+class _FormDataFactoryProvider {
+
+  factory FormData([HTMLFormElement form = null]) native '''
+    if (form == null) return new FormData();
+    return new FormData(form);
+  ''';
+
+}
+
 class _WebKitPointFactoryProvider {
 
   factory WebKitPoint(num x, num y) native '''return new WebKitPoint(x, y);''';