Fix popup crash on ChromeOS.

ui/message_center/views/message_popup_collection.cc

Index: ui/message_center/views/message_popup_collection.cc
diff --git a/ui/message_center/views/message_popup_collection.cc b/ui/message_center/views/message_popup_collection.cc
index 541963e602d1e5cf3ce6ae4f62d73afc66b752c9..2474ad00e63b7f417339d089ce2fab083343190c 100644
--- a/ui/message_center/views/message_popup_collection.cc
+++ b/ui/message_center/views/message_popup_collection.cc
@@ -101,6 +101,10 @@ MessagePopupCollection::~MessagePopupCollection() {
   screen->RemoveObserver(this);
   message_center_->RemoveObserver(this);
 
+  CloseAllWidgets();
+}
+
+void MessagePopupCollection::MarkAllPopupsShown() {
   std::set<std::string> closed_ids = CloseAllWidgets();
   for (std::set<std::string>::iterator iter = closed_ids.begin();
        iter != closed_ids.end(); iter++) {