gn: Use a separate flag for enabling libgnome-keyring support.

components/os_crypt/features.gni

Index: components/os_crypt/features.gni
diff --git a/components/os_crypt/features.gni b/components/os_crypt/features.gni
new file mode 100644
index 0000000000000000000000000000000000000000..f67c8b9728d067473d0d2ac681bedfed33bcb629
--- /dev/null
+++ b/components/os_crypt/features.gni
@@ -0,0 +1,11 @@
+# Copyright 2016 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.
+
+import("//build/config/ui.gni")
+
+declare_args() {
+  # Whether to use libgnome-keyring (deprecated by libsecret).
+  # See http://crbug.com/466975 and http://crbug.com/355223.
+  use_gnome_keyring = is_desktop_linux && use_glib
+}