Added CHECKs for null pointers in ChromeAppSorting.

extensions/browser/app_sorting.h

Index: extensions/browser/app_sorting.h
diff --git a/extensions/browser/app_sorting.h b/extensions/browser/app_sorting.h
index 39d50dcd16c45c4393ac9dfc054a9b498d88a7d9..bc6378db30536d1643bbacafee4d06126655efde 100644
--- a/extensions/browser/app_sorting.h
+++ b/extensions/browser/app_sorting.h
@@ -27,11 +27,17 @@ class AppSorting {
   // caller.
   virtual void SetExtensionScopedPrefs(ExtensionScopedPrefs* prefs) = 0;
 
+  // CHECKs that SetExtensionScopedPrefs has been called with a non-null object.
+  // TODO(mgiuca): Added this to try and diagnose http://crbug.com/476648.
+  // Remove it after the investigation is concluded.
+  virtual void CheckExtensionScopedPrefs() const = 0;
+
   // Sets up the ExtensionSyncService to inform of changes that require syncing.
   virtual void SetExtensionSyncService(
       ExtensionSyncService* extension_sync_service) = 0;
 
   // Properly initializes internal values that require |extension_ids|.
+  // SetExtensionScopedPrefs must have been called prior to this.
   virtual void Initialize(const extensions::ExtensionIdList& extension_ids) = 0;
 
   // Resolves any conflicts the might be created as a result of syncing that