Remove content::NotificationObserver dependency from most Prefs code.

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

Index: chrome/browser/ui/webui/ntp/ntp_login_handler.h
diff --git a/chrome/browser/ui/webui/ntp/ntp_login_handler.h b/chrome/browser/ui/webui/ntp/ntp_login_handler.h
index 331caf9ec2dc53c1150aa3200575d6aded2326a9..a00b313c58fd3adef415c6338bf9d76612f09607 100644
--- a/chrome/browser/ui/webui/ntp/ntp_login_handler.h
+++ b/chrome/browser/ui/webui/ntp/ntp_login_handler.h
@@ -5,6 +5,7 @@
 #ifndef CHROME_BROWSER_UI_WEBUI_NTP_NTP_LOGIN_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_NTP_NTP_LOGIN_HANDLER_H_
 
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -16,7 +17,8 @@ class Profile;
 // username at the top of the NTP (and update itself when that changes).
 // In the future it may expand to allow users to login from the NTP.
 class NTPLoginHandler : public content::WebUIMessageHandler,
-                        public content::NotificationObserver {
+                        public content::NotificationObserver,
+                        public PrefObserver {
  public:
   NTPLoginHandler();
   virtual ~NTPLoginHandler();
@@ -29,6 +31,10 @@ class NTPLoginHandler : public content::WebUIMessageHandler,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver interface
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Returns true if the login handler should be shown in a new tab page
   // for the given |profile|. |profile| must not be NULL.
   static bool ShouldShow(Profile* profile);