Update first download notification correctly if there are multiple notifications

chrome/browser/download/notification/download_notification_manager.h

Index: chrome/browser/download/notification/download_notification_manager.h
diff --git a/chrome/browser/download/notification/download_notification_manager.h b/chrome/browser/download/notification/download_notification_manager.h
index dbc84e86dfe2c016b4275fad842373331c25859b..7490c1a0396dd0923b7e81dc37341eb737e2bff4 100644
--- a/chrome/browser/download/notification/download_notification_manager.h
+++ b/chrome/browser/download/notification/download_notification_manager.h
@@ -45,6 +45,10 @@ class DownloadNotificationManagerForProfile
       Profile* profile, DownloadNotificationManager* parent_manager);
   ~DownloadNotificationManagerForProfile() override;
 
+  message_center::MessageCenter* message_center() const {
+    return message_center_;
+  }
+
   // DownloadItem::Observer overrides:
   void OnDownloadUpdated(content::DownloadItem* download) override;
   void OnDownloadOpened(content::DownloadItem* download) override;
@@ -56,11 +60,17 @@ class DownloadNotificationManagerForProfile
  private:
   friend class test::DownloadItemNotificationTest;
 
+  void OverrideMessageCenterForTest(
+      message_center::MessageCenter* message_center);
+
   Profile* profile_ = nullptr;
   DownloadNotificationManager* parent_manager_;  // weak
   std::set<content::DownloadItem*> downloading_items_;
   std::map<content::DownloadItem*, DownloadItemNotification*> items_;
 
+  // Pointer to the message center instance.
+  message_center::MessageCenter* message_center_;
+
   STLValueDeleter<std::map<content::DownloadItem*, DownloadItemNotification*>>
       items_deleter_;
 };