Add best-effort/allow rollback flags on WorkItem.

chrome/installer/util/set_reg_value_work_item.h

Index: chrome/installer/util/set_reg_value_work_item.h
diff --git a/chrome/installer/util/set_reg_value_work_item.h b/chrome/installer/util/set_reg_value_work_item.h
index 60104c4e9c89133231adac143a241456c73f498a..c8fdc2b8b935706915f49e46910e56f60fab0fe5 100644
--- a/chrome/installer/util/set_reg_value_work_item.h
+++ b/chrome/installer/util/set_reg_value_work_item.h
@@ -49,10 +49,6 @@ class SetRegValueWorkItem : public WorkItem {
 
   ~SetRegValueWorkItem() override;
 
-  bool Do() override;
-
-  void Rollback() override;
-
  private:
   enum SettingStatus {
     // The status before Do is called.
@@ -70,6 +66,10 @@ class SetRegValueWorkItem : public WorkItem {
     VALUE_ROLL_BACK
   };
 
+  // WorkItem:
+  bool DoImpl() override;
+  void RollbackImpl() override;
+
   // Root key of the target key under which the value is set. The root key can
   // only be one of the predefined keys on Windows.
   HKEY predefined_root_;