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

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 029eeef7bd90e35dfe944f39680cd85ef5919484..0b15a6a599f2d19cc6c398da71c7b409e91cefb3 100644
--- a/ui/message_center/views/notification_view.cc
+++ b/ui/message_center/views/notification_view.cc
@@ -388,7 +388,7 @@ void NotificationView::ButtonPressed(views::Button* sender,
   }
 
   if (sender == settings_button_view_) {
-    controller()->ClickOnSettingsButton(id);
+    OnSettingsButtonPressed();
     return;
   }