Fixed redundant download completed observer updates

We should be careful to not let the same download completion update
surface twice to the UI layer. Otherwise it might inadvertently
introduce duplicate notification bugs.

Bug : 949941

Change-Id: I161066f81fd6d12afb57236847d9d6c47fb2984a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1555653
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649340}

chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java

@@ -254,7 +254,7 @@ public class DownloadNotificationService {
         startTrackingInProgressDownload(id);
     }
 
-    public void cancelNotification(int notificationId) {
+    private void cancelNotification(int notificationId) {
         // TODO(b/65052774): Add back NOTIFICATION_NAMESPACE when able to.
         mNotificationManager.cancel(notificationId);
     }

chrome/browser/download/download_offline_content_provider.cc

@@ -264,6 +264,13 @@ void DownloadOfflineContentProvider::OnDownloadUpdated(DownloadItem* item) {
 
   if (item->GetState() == DownloadItem::COMPLETE) {
     // TODO(crbug.com/938152): May be move this to DownloadItem.
+    if (completed_downloads_.find(item->GetGuid()) !=
+        completed_downloads_.end()) {
+      return;
+    }
+
+    completed_downloads_.insert(item->GetGuid());
+
     AddCompletedDownload(item);
   }
 
@@ -283,12 +290,12 @@ void DownloadOfflineContentProvider::OnDownloadRemoved(DownloadItem* item) {
     observer.OnItemRemoved(contentId);
 }
 
+void DownloadOfflineContentProvider::OnDownloadDestroyed(DownloadItem* item) {
+  completed_downloads_.erase(item->GetGuid());
+}
+
 void DownloadOfflineContentProvider::AddCompletedDownload(DownloadItem* item) {
 #if defined(OS_ANDROID)
-  if (completed_downloads_.find(item->GetGuid()) != completed_downloads_.end())
-    return;
-  completed_downloads_.insert(item->GetGuid());
-
   DownloadManagerBridge::AddCompletedDownload(
       item,
       base::BindOnce(&DownloadOfflineContentProvider::AddCompletedDownloadDone,

chrome/browser/download/download_offline_content_provider.h

@@ -70,6 +70,7 @@ class DownloadOfflineContentProvider : public OfflineContentProvider,
   // DownloadItem::Observer overrides
   void OnDownloadUpdated(DownloadItem* item) override;
   void OnDownloadRemoved(DownloadItem* item) override;
+  void OnDownloadDestroyed(DownloadItem* download) override;
 
   // DownloadManager::Observer overrides
   void ManagerGoingDown(DownloadManager* manager) override;