Remove NOTIFICATION_SYSTEM_SETTING_CHANGED, switch CrosSettings to base::CallbackRegistry.

chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h

Index: chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
diff --git a/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h b/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
index d73db1bb33db7f82869c0bd2d8a163c12a3955f7..4b823b426ebf6dfec4333014d4709b9c46ca0b16 100644
--- a/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
+++ b/chrome/browser/ui/webui/options/chromeos/core_chromeos_options_handler.h
@@ -5,7 +5,11 @@
 #ifndef CHROME_BROWSER_UI_WEBUI_OPTIONS_CHROMEOS_CORE_CHROMEOS_OPTIONS_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_OPTIONS_CHROMEOS_CORE_CHROMEOS_OPTIONS_HANDLER_H_
 
+#include <map>
+
 #include "base/compiler_specific.h"
+#include "base/memory/linked_ptr.h"
+#include "chrome/browser/chromeos/settings/cros_settings.h"
 #include "chrome/browser/chromeos/ui_proxy_config_service.h"
 #include "chrome/browser/ui/webui/options/core_options_handler.h"
 
@@ -32,11 +36,6 @@ class CoreChromeOSOptionsHandler : public ::options::CoreOptionsHandler {
   virtual void GetLocalizedValues(
       base::DictionaryValue* localized_strings) OVERRIDE;
 
-  // content::NotificationObserver implementation.
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) OVERRIDE;
-
  private:
   virtual void OnPreferenceChanged(PrefService* service,
                                    const std::string& pref_name) OVERRIDE;
@@ -46,9 +45,13 @@ class CoreChromeOSOptionsHandler : public ::options::CoreOptionsHandler {
   void SelectNetworkCallback(const base::ListValue* args);
 
   // Notifies registered JS callbacks on ChromeOS setting change.
-  void NotifySettingsChanged(const std::string* setting_name);
+  void NotifySettingsChanged(const std::string& setting_name);
   void NotifyProxyPrefsChanged();
 
+  typedef std::map<std::string, linked_ptr<CrosSettings::ObserverSubscription> >
+      SubscriptionMap;
+  SubscriptionMap pref_subscription_map_;
+
   UIProxyConfigService proxy_config_service_;
 };