[Notifications] Fix swipe to close for ARC notifications.

ui/message_center/views/custom_notification_view.cc

Index: ui/message_center/views/custom_notification_view.cc
diff --git a/ui/message_center/views/custom_notification_view.cc b/ui/message_center/views/custom_notification_view.cc
index a648f83614afb3ca42dddeb698fcfd7f6ab7c35d..1150e5028f587a90653abbf77af30c9398659260 100644
--- a/ui/message_center/views/custom_notification_view.cc
+++ b/ui/message_center/views/custom_notification_view.cc
@@ -90,6 +90,11 @@ void CustomNotificationView::UpdateControlButtonsVisibility() {
     contents_view_delegate_->UpdateControlButtonsVisibility();
 }
 
+void CustomNotificationView::OnSlideChanged() {
+  if (contents_view_delegate_)
+    contents_view_delegate_->OnSlideChanged();
+}
+
 gfx::Size CustomNotificationView::GetPreferredSize() const {
   const gfx::Insets insets = GetInsets();
   const int contents_width = kNotificationWidth - insets.width();