Call UpdateControlButtonsVisibility() in OnMouseMoved().

ui/message_center/views/notification_view.cc

Index: ui/message_center/views/notification_view.cc
diff --git a/ui/message_center/views/notification_view.cc b/ui/message_center/views/notification_view.cc
index 1258273003f21b3a5817d84953633ff110145fd0..12b40b608b65ce77493497070a4c8ed4e7638599 100644
--- a/ui/message_center/views/notification_view.cc
+++ b/ui/message_center/views/notification_view.cc
@@ -346,6 +346,11 @@ gfx::NativeCursor NotificationView::GetCursor(const ui::MouseEvent& event) {
   return views::GetNativeHandCursor();
 }
 
+void NotificationView::OnMouseMoved(const ui::MouseEvent& event) {
+  MessageView::OnMouseMoved(event);
+  UpdateControlButtonsVisibility();
+}
+
 void NotificationView::OnMouseEntered(const ui::MouseEvent& event) {
   MessageView::OnMouseEntered(event);
   UpdateControlButtonsVisibility();