Downloads: Added transient flag to download item and download database

content/public/test/fake_download_item.h

Index: content/public/test/fake_download_item.h
diff --git a/content/public/test/fake_download_item.h b/content/public/test/fake_download_item.h
index cb3e789aae804dedd649f1a0c7c4ef70062cdc4c..6e62bf34941d1248b4102bb96721540e9dfe4da1 100644
--- a/content/public/test/fake_download_item.h
+++ b/content/public/test/fake_download_item.h
@@ -120,6 +120,7 @@ class FakeDownloadItem : public DownloadItem {
   bool GetAutoOpened() override;
   bool GetOpened() const override;
   base::Time GetLastAccessTime() const override;
+  bool IsTransient() const override;
   BrowserContext* GetBrowserContext() const override;
   WebContents* GetWebContents() const override;
   void OnContentCheckCompleted(DownloadDangerType danger_type) override;