[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 c20104bf5e764329a415ef0056137ea7b8e46679..bb70458ebb05143f1f7e68edbb591248f70076c9 100644
--- a/ui/message_center/views/custom_notification_view.cc
+++ b/ui/message_center/views/custom_notification_view.cc
@@ -84,6 +84,11 @@ 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();