mash: Add a simple, temporary preferences store.

components/filesystem/public/cpp/prefs/BUILD.gn

Index: components/filesystem/public/cpp/prefs/BUILD.gn
diff --git a/components/filesystem/public/cpp/prefs/BUILD.gn b/components/filesystem/public/cpp/prefs/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..22131db967074b1763c5058b6dee371f7e31abcf
--- /dev/null
+++ b/components/filesystem/public/cpp/prefs/BUILD.gn
@@ -0,0 +1,20 @@
+# 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.
+
+source_set("prefs") {
+  sources = [
+    "filesystem_json_pref_store.cc",
+    "filesystem_json_pref_store.h",
+    "pref_service_factory.cc",
+    "pref_service_factory.h",
+  ]
+
+  deps = [
+    "//base",
+    "//base:prefs",
+    "//components/filesystem/public/interfaces",
+    "//mojo/common",
+    "//mojo/shell/public/cpp",
+  ]
+}