Adds a small icon to notifications, and connects it to synced notifications.

ui/message_center/notification_list.h

Index: ui/message_center/notification_list.h
diff --git a/ui/message_center/notification_list.h b/ui/message_center/notification_list.h
index 3ea8112eb3e34a15da377e395ffba01723294e34..343b20a68ed94d7878d4ecee4efa7c5f9040da08 100644
--- a/ui/message_center/notification_list.h
+++ b/ui/message_center/notification_list.h
@@ -82,6 +82,10 @@ class MESSAGE_CENTER_EXPORT NotificationList {
                                  int button_index,
                                  const gfx::Image& image);
 
+  // Returns true if the notification exists and was updated.
+  bool SetNotificationSmallImage(const std::string& notification_id,
+                                 const gfx::Image& image);
+
   // Returns true if |id| matches a notification in the list.
   bool HasNotification(const std::string& id);