[Downloads] Add referrer URL to browser side on chrome://downloads page

This is intended to replace the currently displayed URL(download URL) on a
downloaditem. It follows the same existing logic as the downloads URL.

UI changes will be made in a follow-up CL.

Bug: 40280033
Change-Id: Idee2863c167974e3e4a3849644ff549b164ceb53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5578496
Reviewed-by: Lily Chen <chlily@chromium.org>
Commit-Queue: Kerry Meng-Lin <kmenglin@google.com>
Reviewed-by: Matthew Denton <mpdenton@chromium.org>
Reviewed-by: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1307749}