Extract the view of control buttons on notification into a separated class

ui/arc/notification/arc_notification_content_view_unittest.cc

Index: ui/arc/notification/arc_notification_content_view_unittest.cc
diff --git a/ui/arc/notification/arc_notification_content_view_unittest.cc b/ui/arc/notification/arc_notification_content_view_unittest.cc
index 1ef1e28f324921097c9295cac465843b5630aa81..6caeba3598b4965f93091f56187373db70f07ce0 100644
--- a/ui/arc/notification/arc_notification_content_view_unittest.cc
+++ b/ui/arc/notification/arc_notification_content_view_unittest.cc
@@ -19,7 +19,8 @@
 #include "ui/message_center/notification.h"
 #include "ui/message_center/views/message_center_controller.h"
 #include "ui/message_center/views/message_view_factory.h"
-#include "ui/views/controls/button/image_button.h"
+#include "ui/message_center/views/notification_control_buttons_view.h"
+#include "ui/message_center/views/padded_button.h"
 #include "ui/views/test/views_test_base.h"
 
 namespace arc {
@@ -241,10 +242,12 @@ class ArcNotificationContentViewTest : public views::ViewsTestBase {
 
   void PressCloseButton() {
     DummyEvent dummy_event;
-    views::ImageButton* close_button =
-        GetArcNotificationContentView()->close_button_.get();
+    auto* control_buttons_view =
+        GetArcNotificationContentView()->control_buttons_view_;
+    message_center::PaddedButton* close_button =
+        control_buttons_view->close_button_for_testing();
     ASSERT_NE(nullptr, close_button);
-    GetArcNotificationContentView()->ButtonPressed(close_button, dummy_event);
+    control_buttons_view->ButtonPressed(close_button, dummy_event);
   }
 
   void CreateAndShowNotificationView(