Correctly show notification timestamp

Adding workaround for keeping
the notification timestamp visible. Invalidating
the layout of the parent view of the timestamp any time
it's visibility is changed.

Bug: 991150
Change-Id: If8c750bfc8f34310a8e93ff2ea30e180e19a9e68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1739976Reviewed-by: Tim Song <tengs@chromium.org>
Reviewed-by: Richard Knoll <knollr@chromium.org>
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685335}

ui/message_center/views/notification_header_view.cc

@@ -404,6 +404,9 @@ void NotificationHeaderView::UpdateSummaryTextVisibility() {
   const bool timestamp_visible = !has_progress_ && timestamp_;
   timestamp_divider_->SetVisible(timestamp_visible);
   timestamp_view_->SetVisible(timestamp_visible);
+
+  // TODO(crbug.com/991492): this should not be necessary.
+  detail_views_->InvalidateLayout();
 }
 
 }  // namespace message_center