Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/webui/ntp/app_launcher_handler.h

Index: chrome/browser/ui/webui/ntp/app_launcher_handler.h
diff --git a/chrome/browser/ui/webui/ntp/app_launcher_handler.h b/chrome/browser/ui/webui/ntp/app_launcher_handler.h
index d91f6ec391b6450f2b2398492215d536abd9aacd..92809303aaa8bdbaa5d922ebff27cbb220d8ca7c 100644
--- a/chrome/browser/ui/webui/ntp/app_launcher_handler.h
+++ b/chrome/browser/ui/webui/ntp/app_launcher_handler.h
@@ -9,6 +9,7 @@
 
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/common/cancelable_request.h"
 #include "chrome/browser/extensions/extension_install_prompt.h"
 #include "chrome/browser/extensions/extension_uninstall_dialog.h"
@@ -32,7 +33,8 @@ class AppNotification;
 class AppLauncherHandler : public content::WebUIMessageHandler,
                            public ExtensionUninstallDialog::Delegate,
                            public ExtensionInstallPrompt::Delegate,
-                           public content::NotificationObserver {
+                           public content::NotificationObserver,
+                           public PrefObserver {
  public:
   explicit AppLauncherHandler(ExtensionService* extension_service);
   virtual ~AppLauncherHandler();
@@ -52,6 +54,10 @@ class AppLauncherHandler : public content::WebUIMessageHandler,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Populate the given dictionary with all installed app info.
   void FillAppDictionary(base::DictionaryValue* value);