Add GN build file for pref_registry component.

I need this for bookmarks component.

Test plan:

$ gn gen out/Debug_gn
$ ninja -C out/Debug_gn pref_registry

In release:

$ gn gen out/Release_gn --args='is_debug=false'
$ ninja -C out/Debug_gn pref_registry

BUG=None
TEST=see above
TBR=brettw@chromium.org,jochen@chromium.org

Review URL: https://codereview.chromium.org/343293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@279773 0039d316-1c4b-4281-b951-d872f2087c98

components/BUILD.gn

@@ -16,6 +16,7 @@ group("all_components") {
     "//components/navigation_metrics",
     "//components/onc",
     "//components/os_crypt",
+    "//components/pref_registry",
     "//components/query_parser",
     "//components/resources:components_resources",
     "//components/startup_metric_utils",

components/pref_registry/BUILD.gn

@@ -0,0 +1,33 @@
+# Copyright 2014 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.
+
+component("pref_registry") {
+  sources = [
+    "pref_registry_export.h",
+    "pref_registry_syncable.cc",
+    "pref_registry_syncable.h",
+  ]
+
+  defines = [
+    "PREF_REGISTRY_IMPLEMENTATION",
+  ]
+
+  deps = [
+    "//base",
+    "//base:prefs",
+    "//base/third_party/dynamic_annotations",
+    "//ui/base",
+  ]
+}
+
+source_set("pref_registry_test_support") {
+  sources = [
+    "testing_pref_service_syncable.cc",
+    "testing_pref_service_syncable.h",
+  ]
+
+  deps = [
+    ":pref_registry",
+  ]
+}