Compile more Gallery targets in gyp v2.

ui/file_manager/gallery/js/gallery_constants.js

Index: ui/file_manager/gallery/js/gallery_constants.js
diff --git a/ui/file_manager/gallery/js/gallery_constants.js b/ui/file_manager/gallery/js/gallery_constants.js
new file mode 100644
index 0000000000000000000000000000000000000000..b2f06090ae198f9b2724825d5595c3b200beae55
--- /dev/null
+++ b/ui/file_manager/gallery/js/gallery_constants.js
@@ -0,0 +1,23 @@
+// Copyright 2017 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.
+
+/**
+ * Modes in Gallery.
+ * @enum {string}
+ */
+var GalleryMode = {
+  SLIDE: 'slide',
+  THUMBNAIL: 'thumbnail'
+};
+
+/**
+ * Sub modes in Gallery.
+ * @enum {string}
+ * TODO(yawano): Remove sub modes by extracting them as modes.
+ */
+var GallerySubMode = {
+  BROWSE: 'browse',
+  EDIT: 'edit',
+  SLIDESHOW: 'slideshow'
+};