Build shadow_dom package in dart/pkg

pkg/shadow_dom/lib/src/platform/platform-init.js

Index: pkg/shadow_dom/lib/src/platform/platform-init.js
diff --git a/tests/language/missing_part_of_tag_part.dart b/pkg/shadow_dom/lib/src/platform/platform-init.js
similarity index 91%
copy from tests/language/missing_part_of_tag_part.dart
copy to pkg/shadow_dom/lib/src/platform/platform-init.js
index c4618bc60b69a7cac8d7ddacd25c37ea3840f96a..4e83afc8c5fafb541d0e44d97fbd3621ddba5040 100644
--- a/tests/language/missing_part_of_tag_part.dart
+++ b/pkg/shadow_dom/lib/src/platform/platform-init.js
@@ -1,3 +1,5 @@
 // Copyright (c) 2013, 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.
+
+var Platform = {};