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..a57813f7ce59fae809e2e2cea1667c0bac1de7aa
--- /dev/null
+++ b/ui/file_manager/gallery/js/gallery_constants.js
@@ -0,0 +1,16 @@
+// 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'};