Remove content::NotificationObserver dependency from most Prefs code.

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 content::NotificationObserver {
+class PreferenceEventRouter : public PrefObserver {
  public:
   explicit PreferenceEventRouter(Profile* profile);
   virtual ~PreferenceEventRouter();
 
  private:
-  // 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;
 
-  void OnPrefChanged(PrefService* pref_service, const std::string& pref_key);
+  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_;
 
   // Weak, owns us (transitively via ExtensionService).
@@ skipping 69 matching lines @@
  protected:
   virtual ~ClearPreferenceFunction();
 
   // ExtensionFunction:
   virtual bool RunImpl() OVERRIDE;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_PREFERENCE_PREFERENCE_API_H__