Add KeyedServiceShutdownNotifier for classes that depend on keyed services but can't be keyed servi…

components/keyed_service/core/keyed_service_shutdown_notifier.cc

+// Copyright 2015 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.
+
+#include "components/keyed_service/core/keyed_service_export.h"
+#include "components/keyed_service/core/keyed_service_shutdown_notifier.h"
+
+KeyedServiceShutdownNotifier::KeyedServiceShutdownNotifier() {
+}
+KeyedServiceShutdownNotifier::~KeyedServiceShutdownNotifier() {
+}
+
+scoped_ptr<base::CallbackList<void()>::Subscription>
+KeyedServiceShutdownNotifier::Subscribe(const base::Closure& callback) {
+  return callback_list_.Add(callback);
+}
+
+void KeyedServiceShutdownNotifier::Shutdown() {
+  callback_list_.Notify();
+}