Clean up pref change notification handling.

chrome/browser/prefs/pref_notifier_impl.h

+// Copyright (c) 2010 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.
+
+#ifndef CHROME_BROWSER_PREFS_PREF_NOTIFIER_IMPL_H_
+#define CHROME_BROWSER_PREFS_PREF_NOTIFIER_IMPL_H_
+#pragma once
+
+#include <string>
+
+#include "base/hash_tables.h"
+#include "base/non_thread_safe.h"
+#include "base/observer_list.h"
+#include "chrome/browser/prefs/pref_notifier.h"
+
+class PrefService;
+class NotificationObserver;
+
+// The PrefNotifier implementation used by the PrefService.
+class PrefNotifierImpl : public PrefNotifier,
+                         public NonThreadSafe {
+ public:
+  explicit PrefNotifierImpl(PrefService* pref_service);
+  virtual ~PrefNotifierImpl();
+
+  // If the pref at the given path changes, we call the observer's Observe
+  // method with PREF_CHANGED.
+  void AddPrefObserver(const char* path, NotificationObserver* obs);
+  void RemovePrefObserver(const char* path, NotificationObserver* obs);
+
+  // PrefNotifier overrides.
+  virtual void OnPreferenceChanged(const std::string& pref_name);
+  virtual void OnInitializationCompleted();
+
+ protected:
+  // A map from pref names to a list of observers. Observers get fired in the
+  // order they are added. These should only be accessed externally for unit
+  // testing.
+  typedef ObserverList<NotificationObserver> NotificationObserverList;
+  typedef base::hash_map<std::string, NotificationObserverList*>
+      PrefObserverMap;
+
+  const PrefObserverMap* pref_observers() const { return &pref_observers_; }
+
+ private:
+  // For the given pref_name, fire any observer of the pref. Virtual so it can
+  // be mocked for unit testing.
+  virtual void FireObservers(const std::string& path);
+
+  // Weak reference; the notifier is owned by the PrefService.
+  PrefService* pref_service_;
+
+  PrefObserverMap pref_observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrefNotifierImpl);
+};
+
+#endif  // CHROME_BROWSER_PREFS_PREF_NOTIFIER_IMPL_H_