Remove PrefObserver usages, batch 12.

chrome/browser/ui/alternate_error_tab_observer.h

Index: chrome/browser/ui/alternate_error_tab_observer.h
diff --git a/chrome/browser/ui/alternate_error_tab_observer.h b/chrome/browser/ui/alternate_error_tab_observer.h
index 071dea8f10a4df504a708c91a2abbaa772de0d6d..9a933b4a554575ceba3d7b096a132db5507cb531 100644
--- a/chrome/browser/ui/alternate_error_tab_observer.h
+++ b/chrome/browser/ui/alternate_error_tab_observer.h
@@ -6,7 +6,6 @@
 #define CHROME_BROWSER_UI_ALTERNATE_ERROR_TAB_OBSERVER_H_
 
 #include "base/prefs/public/pref_change_registrar.h"
-#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -19,8 +18,7 @@ class Profile;
 class AlternateErrorPageTabObserver
     : public content::WebContentsObserver,
       public content::NotificationObserver,
-      public content::WebContentsUserData<AlternateErrorPageTabObserver>,
-      public PrefObserver {
+      public content::WebContentsUserData<AlternateErrorPageTabObserver> {
  public:
   virtual ~AlternateErrorPageTabObserver();
 
@@ -39,16 +37,14 @@ class AlternateErrorPageTabObserver
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
-  // PrefObserver overrides:
-  virtual void OnPreferenceChanged(PrefServiceBase* service,
-                                   const std::string& pref_name) OVERRIDE;
-
   // Internal helpers ----------------------------------------------------------
 
   // Returns the server that can provide alternate error pages.  If the returned
   // URL is empty, the default error page built into WebKit will be used.
   GURL GetAlternateErrorPageURL() const;
 
+  void OnAlternateErrorPagesEnabledChanged();
+
   // Send the alternate error page URL to the renderer.
   void UpdateAlternateErrorPageURL(content::RenderViewHost* rvh);