Update the button visibility when mouse enters or exits from notification surface window

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 67 matching lines @@
     // 1. Touches, because View should no longer receive touch events.
     //    See View::OnTouchEvent.
     // 2. Tap gestures are handled on the Android side, so ignore them.
     //    See crbug.com/709911.
     // 3. Key events. These are already forwarded by NotificationSurface's
     //    WindowDelegate.
     if (event->IsLocatedEvent()) {
       ui::LocatedEvent* located_event = event->AsLocatedEvent();
       located_event->target()->ConvertEventToTarget(widget->GetNativeWindow(),
                                                     located_event);
+      if (located_event->type() == ui::ET_MOUSE_ENTERED ||
+          located_event->type() == ui::ET_MOUSE_EXITED) {
+        owner_->UpdateControlButtonsVisibility();
+        return;
+      }
+
       if (located_event->type() == ui::ET_MOUSE_MOVED) {
         widget->OnMouseEvent(located_event->AsMouseEvent());
       } else if (located_event->IsScrollEvent()) {
         widget->OnScrollEvent(located_event->AsScrollEvent());
       } else if (located_event->IsGestureEvent() &&
                  event->type() != ui::ET_GESTURE_TAP) {
         widget->OnGestureEvent(located_event->AsGestureEvent());
       }
     }
   }
@@ skipping 625 matching lines @@
     }
     if (close_button_) {
       close_button_->set_background(
           views::Background::CreateSolidBackground(current_color));
       close_button_->SchedulePaint();
     }
   }
 }
 
 }  // namespace arc