ArcCustomNotificationView: Fix crash in onBlur

ui/arc/notification/arc_custom_notification_view.cc

Index: ui/arc/notification/arc_custom_notification_view.cc
diff --git a/ui/arc/notification/arc_custom_notification_view.cc b/ui/arc/notification/arc_custom_notification_view.cc
index d0c92d9ecf64e1c90308194caa4c6be580e509dc..8afd6fb8b660219dd3d06e453cd4d24a68a8f7ca 100644
--- a/ui/arc/notification/arc_custom_notification_view.cc
+++ b/ui/arc/notification/arc_custom_notification_view.cc
@@ -534,6 +534,11 @@ void ArcCustomNotificationView::OnFocus() {
 }
 
 void ArcCustomNotificationView::OnBlur() {
+  if (!parent()) {
+    // OnBlur may be called when this view is being removed.
+    return;
+  }
+
   CHECK_EQ(message_center::CustomNotificationView::kViewClassName,
            parent()->GetClassName());