Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/app_list/apps_model_builder.h

Index: chrome/browser/ui/app_list/apps_model_builder.h
diff --git a/chrome/browser/ui/app_list/apps_model_builder.h b/chrome/browser/ui/app_list/apps_model_builder.h
index 5c91583c3d4476504ffbcd2d5fbf0012c1a01897..b943a9ad366d352d87b557a4eb31be39987b3f81 100644
--- a/chrome/browser/ui/app_list/apps_model_builder.h
+++ b/chrome/browser/ui/app_list/apps_model_builder.h
@@ -9,6 +9,7 @@
 
 #include "base/gtest_prod_util.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"
 #include "ui/app_list/app_list_model.h"
@@ -19,6 +20,7 @@ class ExtensionAppItem;
 class Profile;
 
 class AppsModelBuilder : public content::NotificationObserver,
+                         public PrefObserver,
                          public ui::ListModelObserver {
  public:
   AppsModelBuilder(Profile* profile,
@@ -56,6 +58,10 @@ class AppsModelBuilder : public content::NotificationObserver,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // ui::ListModelObserver overrides:
   virtual void ListItemsAdded(size_t start, size_t count) OVERRIDE;
   virtual void ListItemsRemoved(size_t start, size_t count) OVERRIDE;