Downloads: Added transient flag to download item and download database

content/public/test/fake_download_item.cc

Index: content/public/test/fake_download_item.cc
diff --git a/content/public/test/fake_download_item.cc b/content/public/test/fake_download_item.cc
index 4bb1e706a32fb2985eba9f1d06c30c4d19423b5d..e6ffd26362a4585081be19368d711f8573a8d1f5 100644
--- a/content/public/test/fake_download_item.cc
+++ b/content/public/test/fake_download_item.cc
@@ -372,6 +372,11 @@ base::Time FakeDownloadItem::GetLastAccessTime() const {
   return base::Time();
 }
 
+bool FakeDownloadItem::IsTransient() const {
+  NOTREACHED();
+  return true;
+}
+
 BrowserContext* FakeDownloadItem::GetBrowserContext() const {
   NOTREACHED();
   return nullptr;