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

ui/message_center/cocoa/popup_controller_unittest.mm

Index: ui/message_center/cocoa/popup_controller_unittest.mm
diff --git a/ui/message_center/cocoa/popup_controller_unittest.mm b/ui/message_center/cocoa/popup_controller_unittest.mm
index c39d16312888996fcc9d9b0ad27f5c43c788ef0b..e443e04cc291fc9e81267632014f5c307e7eb228 100644
--- a/ui/message_center/cocoa/popup_controller_unittest.mm
+++ b/ui/message_center/cocoa/popup_controller_unittest.mm
@@ -11,6 +11,8 @@
 #import "ui/base/test/ui_cocoa_test_helper.h"
 #include "ui/message_center/notification.h"
 
+namespace message_center {
+
 class PopupControllerTest : public ui::CocoaTest {
 };
 
@@ -41,3 +43,5 @@ TEST_F(PopupControllerTest, Creation) {
   [controller showWindow:nil];
   [controller close];
 }
+
+}  // namespace message_center