Revert of Remove DialogDelegate::OnClosed() which is redundant with

ash/system/chromeos/session/logout_confirmation_dialog.cc

Index: ash/system/chromeos/session/logout_confirmation_dialog.cc
diff --git a/ash/system/chromeos/session/logout_confirmation_dialog.cc b/ash/system/chromeos/session/logout_confirmation_dialog.cc
index 89c73b02476477bb35b58aed301c7faf8d1f3c32..80a71e84248a1dfda9e6b56a231dcaef55168f49 100644
--- a/ash/system/chromeos/session/logout_confirmation_dialog.cc
+++ b/ash/system/chromeos/session/logout_confirmation_dialog.cc
@@ -84,9 +84,13 @@
   return views::DialogDelegateView::GetDialogButtonLabel(button);
 }
 
-void LogoutConfirmationDialog::WindowClosing() {
+void LogoutConfirmationDialog::OnClosed() {
   update_timer_.Stop();
   controller_->OnDialogClosed();
+}
+
+void LogoutConfirmationDialog::DeleteDelegate() {
+  delete this;
 }
 
 void LogoutConfirmationDialog::UpdateLabel() {