Support notifications with custom content

ui/message_center/notification_delegate.cc

Index: ui/message_center/notification_delegate.cc
diff --git a/ui/message_center/notification_delegate.cc b/ui/message_center/notification_delegate.cc
index dd0d54b52d3c6744c3736fe546ef3cb79fb19c91..0cac41da1aa360a23c6bb9b5a8016fc6e4fcbe02 100644
--- a/ui/message_center/notification_delegate.cc
+++ b/ui/message_center/notification_delegate.cc
@@ -4,6 +4,8 @@
 
 #include "ui/message_center/notification_delegate.h"
 
+#include "ui/views/view.h"
+
 namespace message_center {
 
 // NotificationDelegate:
@@ -24,6 +26,10 @@ bool NotificationDelegate::ShouldDisplaySettingsButton() {
   return false;
 }
 
+std::unique_ptr<views::View> NotificationDelegate::CreateCustomContent() {
+  return std::unique_ptr<views::View>();
+}
+
 // HandleNotificationClickedDelegate:
 
 HandleNotificationClickedDelegate::HandleNotificationClickedDelegate(