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,
+                                             Observer* observer)
+    : policy_service_(policy_service),
+      domain_(domain),
+      component_id_(component_id),
+      observer_(observer) {}
+
+PolicyChangeRegistrar::~PolicyChangeRegistrar() {
+  if (!observing_.empty())
+    policy_service_->RemoveObserver(domain_, component_id_, this);
+}
+
+void PolicyChangeRegistrar::Add(const std::string& policy_name) {
+  if (observing_.empty())
+    policy_service_->AddObserver(domain_, component_id_, this);
+  observing_.insert(policy_name);
+}
+
+void PolicyChangeRegistrar::Remove(const std::string& policy_name) {
+  observing_.erase(policy_name);
+  if (observing_.empty())
+    policy_service_->RemoveObserver(domain_, component_id_, this);
+}
+
+void PolicyChangeRegistrar::OnPolicyUpdated(PolicyDomain domain,
+                                            const std::string& component_id,
+                                            const PolicyMap& previous,
+                                            const PolicyMap& current) {
+  for (std::set<std::string>::iterator it = observing_.begin();
+       it != observing_.end(); ++it) {
+    const Value* prev = previous.GetValue(*it);
+    const Value* cur = current.GetValue(*it);
+    if (!base::Value::Equals(prev, cur)) {
+      observer_->OnPolicyValueUpdated(
+          domain_, component_id_, *it, prev, cur);
+    }
+  }
+}
+
+}  // namespace policy