Add stub for dart:nativewrappers library.

lib/html/dartium/nativewrappers.dart

Index: lib/html/dartium/nativewrappers.dart
diff --git a/lib/html/dartium/nativewrappers.dart b/lib/html/dartium/nativewrappers.dart
new file mode 100644
index 0000000000000000000000000000000000000000..44ab39e1ac7567e620f8402b566e4b492836d41e
--- /dev/null
+++ b/lib/html/dartium/nativewrappers.dart
@@ -0,0 +1,8 @@
+// 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.
+
+#library('nativewrappers');
+
+class NativeFieldWrapperClass1 {
+}