Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/ui/app_list/apps_model_builder.cc

Index: chrome/browser/ui/app_list/apps_model_builder.cc
diff --git a/chrome/browser/ui/app_list/apps_model_builder.cc b/chrome/browser/ui/app_list/apps_model_builder.cc
index 9eb65a270ee27fd60d3964ec08b3d9b624542dd7..8dba307902e4e33659fc86e2911fad3760bba9bb 100644
--- a/chrome/browser/ui/app_list/apps_model_builder.cc
+++ b/chrome/browser/ui/app_list/apps_model_builder.cc
@@ -208,15 +208,16 @@ void AppsModelBuilder::Observe(int type,
       HighlightApp();
       break;
     }
-    case chrome::NOTIFICATION_PREF_CHANGED: {
-      ResortApps();
-      break;
-    }
     default:
       NOTREACHED();
   }
 }
 
+void AppsModelBuilder::OnPreferenceChanged(PrefServiceBase* service,
+                                           const std::string& pref_name) {
+  ResortApps();
+}
+
 void AppsModelBuilder::ListItemsAdded(size_t start, size_t count) {
 }