Added PolicyChangeRegistrar, to observe specific policies at the PolicyService.

chrome/browser/policy/policy_service.cc

+// Copyright (c) 2012 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 "chrome/browser/policy/policy_service.h"
+
+#include "base/values.h"
+
+namespace policy {
+
+PolicyChangeRegistrar::PolicyChangeRegistrar(PolicyService* policy_service,
+                                             PolicyDomain domain,
+                                             const std::string component_id)
+    : policy_service_(policy_service),
+      domain_(domain),
+      component_id_(component_id) {}
+
+PolicyChangeRegistrar::~PolicyChangeRegistrar() {
+  if (!callback_map_.empty())
+    policy_service_->RemoveObserver(domain_, component_id_, this);
+}
+
+void PolicyChangeRegistrar::Observe(const std::string& policy_name,
+                                    const UpdateCallback& callback) {
+  if (callback_map_.empty())
+    policy_service_->AddObserver(domain_, component_id_, this);
+  callback_map_[policy_name] = callback;
+}
+
+void PolicyChangeRegistrar::OnPolicyUpdated(PolicyDomain domain,
+                                            const std::string& component_id,
+                                            const PolicyMap& previous,
+                                            const PolicyMap& current) {
+  for (CallbackMap::iterator it = callback_map_.begin();
+       it != callback_map_.end(); ++it) {
+    const Value* prev = previous.GetValue(it->first);
+    const Value* cur = current.GetValue(it->first);
+    if (!base::Value::Equals(prev, cur))
+      it->second.Run(prev, cur);
+  }
+}
+
+}  // namespace policy