Add script files of the separated Gallery.app.

ui/file_manager/gallery/js/metadata_worker.js

Index: ui/file_manager/gallery/js/metadata_worker.js
diff --git a/ui/file_manager/gallery/js/metadata_worker.js b/ui/file_manager/gallery/js/metadata_worker.js
new file mode 100644
index 0000000000000000000000000000000000000000..8354602c7e170576510b8704692b1abfe2d192bd
--- /dev/null
+++ b/ui/file_manager/gallery/js/metadata_worker.js
@@ -0,0 +1,10 @@
+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+'use strict';
+
+// Load the worker script of Files.app.
+importScripts(
+    'chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/' +
+    'foreground/js/metadata/metadata_dispatcher.js');