Add best-effort/allow rollback flags on WorkItem.

chrome/installer/util/delete_reg_key_work_item.cc

Index: chrome/installer/util/delete_reg_key_work_item.cc
diff --git a/chrome/installer/util/delete_reg_key_work_item.cc b/chrome/installer/util/delete_reg_key_work_item.cc
index 9f482311037ffe99013136d97d75e2a730913278..b0ba01961093eee625e0932652d6febe999c87a9 100644
--- a/chrome/installer/util/delete_reg_key_work_item.cc
+++ b/chrome/installer/util/delete_reg_key_work_item.cc
@@ -29,14 +29,16 @@ DeleteRegKeyWorkItem::DeleteRegKeyWorkItem(HKEY predefined_root,
          wow64_access == KEY_WOW64_64KEY);
 }
 
-bool DeleteRegKeyWorkItem::Do() {
+bool DeleteRegKeyWorkItem::DoImpl() {
+  DCHECK(!key_deleted_);
+
   if (path_.empty())
     return false;
 
   RegistryKeyBackup backup;
 
-  // Only try to make a backup if we're not configured to ignore failures.
-  if (!ignore_failure_) {
+  // Only try to make a backup if rollback is allowed.
+  if (allow_rollback()) {
     if (!backup.Initialize(predefined_root_, path_.c_str(), wow64_access_)) {
       LOG(ERROR) << "Failed to backup destination for registry key copy.";
       return false;
@@ -46,17 +48,18 @@ bool DeleteRegKeyWorkItem::Do() {
   // Delete the key.
   if (!InstallUtil::DeleteRegistryKey(
           predefined_root_, path_.c_str(), wow64_access_)) {
-    return ignore_failure_;
+    return false;
   }
 
   // We've succeeded, so remember any backup we may have made.
   backup_.swap(backup);
 
+  key_deleted_ = true;
   return true;
 }
 
-void DeleteRegKeyWorkItem::Rollback() {
-  if (ignore_failure_)
+void DeleteRegKeyWorkItem::RollbackImpl() {
+  if (!key_deleted_)
     return;
 
   // Delete anything in the key before restoring the backup in case someone else