Remove the last usages of PrefObserver outside of Prefs.

chrome/browser/ui/cocoa/extensions/extension_action_context_menu.mm

 // 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.
 
 #import "chrome/browser/ui/cocoa/extensions/extension_action_context_menu.h"
 
 #include "base/prefs/public/pref_change_registrar.h"
 #include "base/sys_string_conversions.h"
 #include "chrome/browser/extensions/extension_action.h"
 #include "chrome/browser/extensions/extension_action_manager.h"
@@ skipping 71 matching lines @@
 @interface ExtensionActionContextMenu(Private)
 // Callback for the context menu items.
 - (void)dispatch:(id)menuItem;
 
 // Runs the action for |menuItem|.
 - (void)updateInspectorItem;
 @end
 
 namespace extension_action_context_menu {
 
-class DevmodeObserver : public PrefObserver {
+class DevmodeObserver {
  public:
   DevmodeObserver(ExtensionActionContextMenu* menu,
                   PrefService* service)
       : menu_(menu), pref_service_(service) {
     registrar_.Init(pref_service_);
-    registrar_.Add(prefs::kExtensionsUIDeveloperMode, this);
+    registrar_.Add(
+        prefs::kExtensionsUIDeveloperMode,
+        base::Bind(&DevmodeObserver::OnExtensionsUIDeveloperModeChanged,
+                   base::Unretained(this)));
   }
   virtual ~DevmodeObserver() {}
 
-  void OnPreferenceChanged(PrefServiceBase* service,
-                           const std::string& pref_name) {
+  void OnExtensionsUIDeveloperModeChanged() {
     [menu_ updateInspectorItem];
   }
 
  private:
   ExtensionActionContextMenu* menu_;
   PrefService* pref_service_;
   PrefChangeRegistrar registrar_;
 };
 
 }  // namespace extension_action_context_menu
@@ skipping 165 matching lines @@
 
 - (BOOL)validateMenuItem:(NSMenuItem*)menuItem {
   if ([menuItem tag] == kExtensionContextOptions) {
     // Disable 'Options' if there are no options to set.
     return extension_->options_url().spec().length() > 0;
   }
   return YES;
 }
 
 @end