Pref service: create service at browser startup

services/preferences/BUILD.gn

Index: services/preferences/BUILD.gn
diff --git a/services/preferences/BUILD.gn b/services/preferences/BUILD.gn
index 8640a9194ee55c9b44ec04a8d23edbca2a15ee48..58a2d4ae1ced20fdc57c76f449e189d30b3a8f1e 100644
--- a/services/preferences/BUILD.gn
+++ b/services/preferences/BUILD.gn
@@ -2,9 +2,16 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//services/service_manager/public/service_manifest.gni")
+
 group("tests") {
   testonly = true
   deps = [
     "//services/preferences/public/cpp/tests",
   ]
 }
+
+service_manifest("manifest") {
+  name = "preferences2"
+  source = "manifest.json"
+}