Add best-effort/allow rollback flags on WorkItem.

chrome/installer/util/callback_work_item.cc

Index: chrome/installer/util/callback_work_item.cc
diff --git a/chrome/installer/util/callback_work_item.cc b/chrome/installer/util/callback_work_item.cc
index e2dbbec3ab9f89744c3f444764938d86cf119cd0..34376eab71e5388f73ef2cadb2621c0b583c5c24 100644
--- a/chrome/installer/util/callback_work_item.cc
+++ b/chrome/installer/util/callback_work_item.cc
@@ -17,7 +17,7 @@ CallbackWorkItem::CallbackWorkItem(
 CallbackWorkItem::~CallbackWorkItem() {
 }
 
-bool CallbackWorkItem::Do() {
+bool CallbackWorkItem::DoImpl() {
   DCHECK_EQ(roll_state_, RS_UNDEFINED);
 
   roll_state_ = RS_FORWARD;
@@ -27,7 +27,7 @@ bool CallbackWorkItem::Do() {
   return result;
 }
 
-void CallbackWorkItem::Rollback() {
+void CallbackWorkItem::RollbackImpl() {
   DCHECK_EQ(roll_state_, RS_UNDEFINED);
 
   roll_state_ = RS_BACKWARD;