Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/extensions/external_policy_loader.h

Index: chrome/browser/extensions/external_policy_loader.h
diff --git a/chrome/browser/extensions/external_policy_loader.h b/chrome/browser/extensions/external_policy_loader.h
index bd0f5f5684d132ecc79eb6704708783c205b4592..44f9f1b1cdf6d89d500da2419cd8bb1e090fbb93 100644
--- a/chrome/browser/extensions/external_policy_loader.h
+++ b/chrome/browser/extensions/external_policy_loader.h
@@ -9,6 +9,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/prefs/public/pref_change_registrar.h"
+#include "base/prefs/public/pref_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
@@ -21,7 +22,8 @@ namespace extensions {
 // registered.
 class ExternalPolicyLoader
     : public ExternalLoader,
-      public content::NotificationObserver {
+      public content::NotificationObserver,
+      public PrefObserver {
  public:
   explicit ExternalPolicyLoader(Profile* profile);
 
@@ -30,6 +32,10 @@ class ExternalPolicyLoader
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver implementation
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
  protected:
   virtual void StartLoading() OVERRIDE;