Clean up pref change notification handling.

chrome/common/pref_store_base.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_COMMON_PREF_STORE_BASE_H_
+#define CHROME_COMMON_PREF_STORE_BASE_H_
+#pragma once
+
+#include "base/observer_list.h"
+#include "chrome/common/pref_store.h"
+
+// Implements the observer-related bits of the PrefStore interface. This is
+// provided as a convenience for PrefStore implementations to derive from.
+class PrefStoreBase : public PrefStore {
+ public:
+  virtual ~PrefStoreBase() {}
+
+  // Overriden from PrefStore.
+  virtual void AddObserver(ObserverInterface* observer);
+  virtual void RemoveObserver(ObserverInterface* observer);
+
+ protected:
+  // Send a notification about a changed preference value.
+  virtual void NotifyPrefValueChanged(const std::string& key);
+
+  // Notify observers about initialization being complete.
+  virtual void NotifyInitializationCompleted();
+
+ private:
+  ObserverList<ObserverInterface, true> observers_;
+};
+
+#endif  // CHROME_COMMON_PREF_STORE_BASE_H_