Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/webui/options/media_galleries_handler.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/ui/webui/options/media_galleries_handler.h"
 
 #include "base/bind.h"
 #include "base/string_number_conversions.h"
 #include "chrome/browser/media_gallery/media_file_system_registry.h"
 #include "chrome/browser/media_gallery/media_galleries_preferences.h"
@@ skipping 112 matching lines @@
 }
 
 void MediaGalleriesHandler::FileSelected(
     const FilePath& path, int index, void* params) {
   chrome::MediaGalleriesPreferences* prefs =
       chrome::MediaFileSystemRegistry::GetInstance()->GetPreferences(
           Profile::FromWebUI(web_ui()));
   prefs->AddGalleryByPath(path);
 }
 
-void MediaGalleriesHandler::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
-  if (type == chrome::NOTIFICATION_PREF_CHANGED &&
-      *content::Details<std::string>(details).ptr() ==
-          prefs::kMediaGalleriesRememberedGalleries) {
-    OnGalleriesChanged();
-  } else {
-    NOTREACHED();
-  }
+void MediaGalleriesHandler::OnPreferenceChanged(PrefServiceBase* service,
+                                                const std::string& pref_name) {
+  DCHECK_EQ(std::string(prefs::kMediaGalleriesRememberedGalleries), pref_name);
+  OnGalleriesChanged();
 }
 
 }  // namespace options