mac: Fix a dangling delegate bug with MCPopupController.

ui/message_center/cocoa/popup_collection.mm

Index: ui/message_center/cocoa/popup_collection.mm
diff --git a/ui/message_center/cocoa/popup_collection.mm b/ui/message_center/cocoa/popup_collection.mm
index dfdf1087acee66601f4f6e76faee17be71cffde7..5961e61409b7eb244259e8a598784dd0ecc815f2 100644
--- a/ui/message_center/cocoa/popup_collection.mm
+++ b/ui/message_center/cocoa/popup_collection.mm
@@ -192,8 +192,8 @@ class PopupCollectionObserver : public message_center::MessageCenterObserver {
     return YES;
   }
 
-  // The popup cannot fit on screen, so it has to be released now.
-  [popup release];
+  // The popup cannot fit on screen, so it has to be closed now.
+  [popup close];
   return NO;
 }