Dark Mode: make downloads item separator border fully opaque

Request from Namrata.

R=aee@chromium.org
BUG=883049

Change-Id: I0421fa21a9d9cb3b7b543b131437142f8dbb176f
Reviewed-on: https://chromium-review.googlesource.com/c/1409921
Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Commit-Queue: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622738}
1 file changed