Remove content::NotificationObserver dependency from most Prefs code.

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

 // 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_NTP_NEW_TAB_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_NTP_NEW_TAB_UI_H_
 
 #include <map>
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/time.h"
 #include "base/timer.h"
 #include "chrome/browser/sessions/tab_restore_service.h"
 #include "chrome/browser/ui/webui/chrome_url_data_manager.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/web_ui_controller.h"
 
 class GURL;
 class PrefService;
 class Profile;
 
 // The WebContents used for the New Tab page.
 class NewTabUI : public content::WebUIController,
-                 public content::NotificationObserver {
+                 public content::NotificationObserver,
+                 public PrefObserver {
  public:
   explicit NewTabUI(content::WebUI* web_ui);
   virtual ~NewTabUI();
 
   static void RegisterUserPrefs(PrefService* prefs);
 
   // Returns whether or not to show apps pages.
   static bool ShouldShowApps();
 
   // Returns whether or not "Discovery" in the NTP is Enabled.
@@ skipping 54 matching lines @@
 
     // Maps resource files to mime types an resource ids.
     std::map<std::string, std::pair<std::string, int> > resource_map_;
 
     DISALLOW_COPY_AND_ASSIGN(NewTabHTMLSource);
   };
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NewTabUITest, UpdateUserPrefsVersion);
 
+  // content::NotificationObserver implementation.
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver implementation.
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Reset the CSS caches.
   void InitializeCSSCaches();
 
   void StartTimingPaint(content::RenderViewHost* render_view_host);
   void PaintTimeout();
 
   Profile* GetProfile() const;
 
   content::NotificationRegistrar registrar_;
 
   // The time when we started benchmarking.
   base::TimeTicks start_;
   // The last time we got a paint notification.
   base::TimeTicks last_paint_;
   // Scoping so we can be sure our timeouts don't outlive us.
   base::OneShotTimer<NewTabUI> timer_;
   // The preference version. This used for migrating prefs of the NTP.
   static const int current_pref_version_ = 3;
 
   // If the sync promo NTP bubble is being shown.
   bool showing_sync_bubble_;
 
   PrefChangeRegistrar pref_change_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(NewTabUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_NTP_NEW_TAB_UI_H_