Do not allow creating dummy notifier id from production, for safety.

ui/message_center/notifier_settings.h

Index: ui/message_center/notifier_settings.h
diff --git a/ui/message_center/notifier_settings.h b/ui/message_center/notifier_settings.h
index cbd2cc32eaab1f6cb90d29e61e31e0b59941fe51..b14e72be96f06e5ae070a72c8c651ab201fad431 100644
--- a/ui/message_center/notifier_settings.h
+++ b/ui/message_center/notifier_settings.h
@@ -7,12 +7,23 @@
 
 #include <string>
 
+#include "base/gtest_prod_util.h"
 #include "base/strings/string16.h"
 #include "ui/gfx/image/image.h"
 #include "ui/message_center/message_center_export.h"
 #include "url/gurl.h"
 
+FORWARD_DECLARE_TEST(MessageCenterTrayBridgeTest,
+                     StatusItemOnlyAfterFirstNotification);
+
+namespace ash {
+class WebNotificationTrayTest;
+}
+
 namespace message_center {
+namespace test {
+class MessagePopupCollectionTest;
+}
 
 class NotifierSettingsDelegate;
 class NotifierSettingsProvider;
@@ -39,9 +50,6 @@ struct MESSAGE_CENTER_EXPORT NotifierId {
   // Constructor for WEB_PAGE type.
   explicit NotifierId(const GURL& url);
 
-  // The default constructor which doesn't specify the notifier. Used for tests.
-  NotifierId();
-
   bool operator==(const NotifierId& other) const;
 
   NotifierType type;
@@ -55,6 +63,22 @@ struct MESSAGE_CENTER_EXPORT NotifierId {
   // The identifier of the profile where the notification is created. This is
   // used for ChromeOS multi-profile support and can be empty.
   std::string profile_id;
+
+ private:
+  friend class MessageCenterTrayTest;
+  friend class test::MessagePopupCollectionTest;
+  friend class NotificationControllerTest;
+  friend class PopupCollectionTest;
+  friend class TrayViewControllerTest;
+  friend class ash::WebNotificationTrayTest;
+  FRIEND_TEST_ALL_PREFIXES(::MessageCenterTrayBridgeTest,
+                           StatusItemOnlyAfterFirstNotification);
+  FRIEND_TEST_ALL_PREFIXES(PopupControllerTest, Creation);
+  FRIEND_TEST_ALL_PREFIXES(NotificationListTest, UnreadCountNoNegative);
+  FRIEND_TEST_ALL_PREFIXES(NotificationListTest, TestHasNotificationOfType);
+
+  // The default constructor which doesn't specify the notifier. Used for tests.
+  NotifierId();
 };
 
 // The struct to hold the information of notifiers. The information will be