Fix popup crash on ChromeOS.

chrome/browser/ui/views/message_center/web_notification_tray.cc

Index: chrome/browser/ui/views/message_center/web_notification_tray.cc
diff --git a/chrome/browser/ui/views/message_center/web_notification_tray.cc b/chrome/browser/ui/views/message_center/web_notification_tray.cc
index 6c6675f6d4712a2918ed4e323d4ab825a0531549..88124f328ae8d67f210a29882c1d2541f1e4b3fa 100644
--- a/chrome/browser/ui/views/message_center/web_notification_tray.cc
+++ b/chrome/browser/ui/views/message_center/web_notification_tray.cc
@@ -152,7 +152,12 @@ bool WebNotificationTray::ShowPopups() {
   return true;
 }
 
-void WebNotificationTray::HidePopups() { popup_collection_.reset(); }
+void WebNotificationTray::HidePopups() {
+  DCHECK(popup_collection_.get());
+
+  popup_collection_->MarkAllPopupsShown();
+  popup_collection_.reset();
+}
 
 bool WebNotificationTray::ShowMessageCenter() {
   message_center_delegate_ =