Fix dangling ddc references in libraries.dart

pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/nativewrappers.dart

Index: pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/nativewrappers.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/nativewrappers.dart b/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/nativewrappers.dart
new file mode 100644
index 0000000000000000000000000000000000000000..bd33769c415c79b121fec232736372c6b923f6fe
--- /dev/null
+++ b/pkg/dev_compiler/tool/input_sdk/lib/html/dart2js/nativewrappers.dart
@@ -0,0 +1,7 @@
+// Copyright (c) 2017, 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.
+
+// This is a dummy library that is referred from dart:io.  It's only used for
+// the VM.
+library dart.nativewrappers;