Add best-effort/allow rollback flags on WorkItem.

chrome/installer/setup/update_active_setup_version_work_item.h

Index: chrome/installer/setup/update_active_setup_version_work_item.h
diff --git a/chrome/installer/setup/update_active_setup_version_work_item.h b/chrome/installer/setup/update_active_setup_version_work_item.h
index bb962aca87a098e8791fa459c91bdc59402d49c1..2a7fb525f886aa49a379631fb3fd5211c5220d8f 100644
--- a/chrome/installer/setup/update_active_setup_version_work_item.h
+++ b/chrome/installer/setup/update_active_setup_version_work_item.h
@@ -43,11 +43,11 @@ class UpdateActiveSetupVersionWorkItem : public WorkItem {
   UpdateActiveSetupVersionWorkItem(const base::string16& active_setup_path,
                                    Operation operation);
 
-  // Overriden from WorkItem.
-  bool Do() override;
-  void Rollback() override;
-
  private:
+  // WorkItem:
+  bool DoImpl() override;
+  void RollbackImpl() override;
+
   // Returns the updated Active Setup version to be used based on the
   // |existing_version|.
   base::string16 GetUpdatedActiveSetupVersion(