ArcCustomNotificationView: Fix crash in onBlur

ui/arc/notification/arc_custom_notification_view.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/arc/notification/arc_custom_notification_view.h"
 
 #include "ash/wm/window_util.h"
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "components/exo/notification_surface.h"
@@ skipping 516 matching lines @@
 void ArcCustomNotificationView::OnFocus() {
   CHECK_EQ(message_center::CustomNotificationView::kViewClassName,
            parent()->GetClassName());
 
   NativeViewHost::OnFocus();
   static_cast<message_center::CustomNotificationView*>(parent())
       ->OnContentFocused();
 }
 
 void ArcCustomNotificationView::OnBlur() {
+  if (!parent()) {
+    // OnBlur may be called when this view is being removed.
+    return;
+  }
+
   CHECK_EQ(message_center::CustomNotificationView::kViewClassName,
            parent()->GetClassName());
 
   NativeViewHost::OnBlur();
   static_cast<message_center::CustomNotificationView*>(parent())
       ->OnContentBlured();
 }
 
 void ArcCustomNotificationView::ActivateToast() {
   if (message_center::ToastContentsView::kViewClassName ==
@@ skipping 80 matching lines @@
 
 void ArcCustomNotificationView::OnNotificationSurfaceRemoved(
     exo::NotificationSurface* surface) {
   if (surface->notification_id() != notification_key_)
     return;
 
   SetSurface(nullptr);
 }
 
 }  // namespace arc