GitLab

Make the path sanitization code in DownloadPrefs more closely match
the version used by ash-chrome (existing chrome for chromeos).

There's still more refactoring work to do to make the behavior
match exactly, but this lets users have a bit more flexibility
with their download location.

Bug: 1148848
Test: added to unit_tests
Change-Id: I54048b60db3191f49187bf7645384f4d2a95218d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566360Reviewed-by: Xing Liu <xingliu@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832485}