Create the control buttons on a notification when showing the buttons if needed.

ui/arc/notification/arc_custom_notification_view.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/arc/notification/arc_custom_notification_view.h"
 
 #include "ash/wm/window_util.h"
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "components/exo/notification_surface.h"
@@ skipping 327 matching lines @@
     const float scale = static_cast<float>(message_center::kNotificationWidth) /
                         preferred_size.width();
     preferred_size.SetSize(message_center::kNotificationWidth,
                            preferred_size.height() * scale);
   }
 
   SetPreferredSize(preferred_size);
 }
 
 void ArcCustomNotificationView::UpdateControlButtonsVisibility() {
-  if (!surface_ || !floating_control_buttons_widget_)
+  if (!surface_)
     return;
 
+  if (!floating_control_buttons_widget_) {
+    if (GetWidget())
+      CreateFloatingControlButtons();
+    else
+      return;
+  }
+
   const bool target_visiblity =
       IsMouseHovered() || (close_button_ && close_button_->HasFocus()) ||
       (settings_button_ && settings_button_->HasFocus());
   if (target_visiblity == floating_control_buttons_widget_->IsVisible())
     return;
 
   if (target_visiblity)
     floating_control_buttons_widget_->Show();
   else
     floating_control_buttons_widget_->Hide();
@@ skipping 259 matching lines @@
 
 void ArcCustomNotificationView::OnNotificationSurfaceRemoved(
     exo::NotificationSurface* surface) {
   if (surface->notification_id() != notification_key_)
     return;
 
   SetSurface(nullptr);
 }
 
 }  // namespace arc