Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/webui/extensions/extension_settings_handler.h

Index: chrome/browser/ui/webui/extensions/extension_settings_handler.h
diff --git a/chrome/browser/ui/webui/extensions/extension_settings_handler.h b/chrome/browser/ui/webui/extensions/extension_settings_handler.h
index 50e0160f9b326279f350d39f02d90c7fe6487d6f..fee671e9a9b5b912bda26bc22dc3b46fa6dea2c4 100644
--- a/chrome/browser/ui/webui/extensions/extension_settings_handler.h
+++ b/chrome/browser/ui/webui/extensions/extension_settings_handler.h
@@ -11,6 +11,7 @@
 
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/extensions/extension_install_ui.h"
 #include "chrome/browser/extensions/extension_uninstall_dialog.h"
 #include "chrome/browser/extensions/extension_warning_set.h"
@@ -59,6 +60,7 @@ struct ExtensionPage {
 class ExtensionSettingsHandler
     : public content::WebUIMessageHandler,
       public content::NotificationObserver,
+      public PrefObserver,
       public content::WebContentsObserver,
       public ui::SelectFileDialog::Listener,
       public ExtensionUninstallDialog::Delegate,
@@ -107,6 +109,10 @@ class ExtensionSettingsHandler
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver implementation.
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // ExtensionUninstallDialog::Delegate implementation, used for receiving
   // notification about uninstall confirmation dialog selections.
   virtual void ExtensionUninstallAccepted() OVERRIDE;