[Reland] Pass the credentials mode to the download service.

This reverts commit 32d5b602.

Diff for the reland:
Fix build file dep issue in:
chrome/browser/ui/webui/download_shelf/BUILD.gn.

Bug: 1239709
Change-Id: Idac32394ac7aede29c01a3a97fa5bf9011f1d1ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3115460


Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Yuheng Huang <yuhengh@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#915631}