Update the background color of ARC notifications when notification settings is opened.

ui/arc/notification/arc_custom_notification_item.h

Index: ui/arc/notification/arc_custom_notification_item.h
diff --git a/ui/arc/notification/arc_custom_notification_item.h b/ui/arc/notification/arc_custom_notification_item.h
index 3a671b9549a4881175dc7f240902bb29a2a70add..f4ed4567b5d4e0f4f8749b9db0acdb540cd5dea5 100644
--- a/ui/arc/notification/arc_custom_notification_item.h
+++ b/ui/arc/notification/arc_custom_notification_item.h
@@ -53,11 +53,16 @@ class ArcCustomNotificationItem : public ArcNotificationItem {
   mojom::ArcNotificationExpandState expand_state() const {
     return expand_state_;
   }
+  mojom::ArcNotificationShownContents shown_contents() const {
+    return shown_contents_;
+  }
 
  private:
   bool pinned_ = false;
   mojom::ArcNotificationExpandState expand_state_ =
       mojom::ArcNotificationExpandState::FIXED_SIZE;
+  mojom::ArcNotificationShownContents shown_contents_ =
+      mojom::ArcNotificationShownContents::CONTENTS_SHOWN;
   gfx::ImageSkia snapshot_;
   int window_ref_count_ = 0;