Parse Attribution interop response URLs as URLs, not origins

This allows us to add coverage for URLs that are not suitable (not
HTTP-family or not potentially trustworthy).

We will add coverage for mixed-suitability redirect chains in a
followup.

Change-Id: I8df7c1f034dc02f031d3f20f34f0602f07c2dead
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5420734


Reviewed-by: Nan Lin <linnan@chromium.org>
Commit-Queue: Andrew Paseltiner <apaseltiner@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282165}