Remove content::NotificationObserver dependency from most Prefs code.

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

Index: chrome/browser/ui/webui/ntp/new_tab_ui.h
diff --git a/chrome/browser/ui/webui/ntp/new_tab_ui.h b/chrome/browser/ui/webui/ntp/new_tab_ui.h
index 0fd64c51527f7666db465942d854eedd7313b17f..59fd481cbc4af6b4a124b481d83222e010b1b33c 100644
--- a/chrome/browser/ui/webui/ntp/new_tab_ui.h
+++ b/chrome/browser/ui/webui/ntp/new_tab_ui.h
@@ -10,6 +10,7 @@
 
 #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"
@@ -24,7 +25,8 @@ 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();
@@ -99,10 +101,15 @@ class NewTabUI : public content::WebUIController,
  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();