Fix popup crash on ChromeOS.

ash/system/web_notification/web_notification_tray_unittest.cc

Index: ash/system/web_notification/web_notification_tray_unittest.cc
diff --git a/ash/system/web_notification/web_notification_tray_unittest.cc b/ash/system/web_notification/web_notification_tray_unittest.cc
index 5ae2e49deaf8612d3fcb5540ba6eb1a62b1d8b66..b64e2b8f7f424cdcf08dfeec5b8b61c86af37057 100644
--- a/ash/system/web_notification/web_notification_tray_unittest.cc
+++ b/ash/system/web_notification/web_notification_tray_unittest.cc
@@ -208,6 +208,16 @@ TEST_F(WebNotificationTrayTest, WebNotificationPopupBubble) {
   // Removing the visible notification should hide the popup bubble.
   RemoveNotification("test_id3");
   EXPECT_FALSE(GetTray()->IsPopupVisible());
+
+  // Now test that we can show multiple popups and then show the message center.
+  AddNotification("test_id4");
+  AddNotification("test_id5");
+  EXPECT_TRUE(GetTray()->IsPopupVisible());
+
+  GetTray()->message_center_tray_->ShowMessageCenterBubble();
+  GetTray()->message_center_tray_->HideMessageCenterBubble();
+
+  EXPECT_FALSE(GetTray()->IsPopupVisible());
 }
 
 using message_center::NotificationList;