Removing PrefObserver usage, batch 4.

chrome/browser/extensions/api/preference/preference_api.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_EXTENSIONS_API_PREFERENCE_PREFERENCE_API_H__
 #define CHROME_BROWSER_EXTENSIONS_API_PREFERENCE_PREFERENCE_API_H__
 
 #include <string>
 
 #include "base/prefs/public/pref_change_registrar.h"
-#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/extensions/extension_function.h"
 #include "content/public/browser/notification_observer.h"
 
 class PrefService;
 
 namespace base {
 class Value;
 }
 
 namespace extensions {
 
-class PreferenceEventRouter : public PrefObserver {
+class PreferenceEventRouter {
  public:
   explicit PreferenceEventRouter(Profile* profile);
   virtual ~PreferenceEventRouter();
 
  private:
-  // PrefObserver implementation.
-  virtual void OnPreferenceChanged(PrefServiceBase* service,
-                                   const std::string& pref_name) OVERRIDE;
-
   void OnPrefChanged(PrefServiceBase* pref_service,
                      const std::string& pref_key);
 
   // This method dispatches events to the extension message service.
   void DispatchEvent(const std::string& extension_id,
                      const std::string& event_name,
                      const std::string& json_args);
 
   PrefChangeRegistrar registrar_;
   PrefChangeRegistrar incognito_registrar_;
@@ skipping 71 matching lines @@
  protected:
   virtual ~ClearPreferenceFunction();
 
   // ExtensionFunction:
   virtual bool RunImpl() OVERRIDE;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_PREFERENCE_PREFERENCE_API_H__