Add best-effort/allow rollback flags on WorkItem.

chrome/installer/util/delete_reg_key_work_item.h

Index: chrome/installer/util/delete_reg_key_work_item.h
diff --git a/chrome/installer/util/delete_reg_key_work_item.h b/chrome/installer/util/delete_reg_key_work_item.h
index 6af588a972c249edd6d618f18efe79a96571486f..524228f887fccb4837f853be3eb2e4aa52187e8f 100644
--- a/chrome/installer/util/delete_reg_key_work_item.h
+++ b/chrome/installer/util/delete_reg_key_work_item.h
@@ -23,10 +23,6 @@ class DeleteRegKeyWorkItem : public WorkItem {
  public:
   ~DeleteRegKeyWorkItem() override;
 
-  bool Do() override;
-
-  void Rollback() override;
-
  private:
   friend class WorkItem;
 
@@ -34,6 +30,10 @@ class DeleteRegKeyWorkItem : public WorkItem {
                        const std::wstring& path,
                        REGSAM wow64_access);
 
+  // WorkItem:
+  bool DoImpl() override;
+  void RollbackImpl() override;
+
   // Root key from which we delete the key. The root key can only be
   // one of the predefined keys on Windows.
   HKEY predefined_root_;
@@ -47,6 +47,9 @@ class DeleteRegKeyWorkItem : public WorkItem {
   // Backup of the deleted key.
   RegistryKeyBackup backup_;
 
+  // True if |backup_| has been initialized.
+  bool backup_initialized_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(DeleteRegKeyWorkItem);
 };