MD Downloads: change a lowercased, no-ink button to an <a>

MD Downloads: change a lowercased, no-ink button to an <a>

This is because it shaves 12 DOM nodes per "Show in Folder"... but it
also looks good as well. Super.

R=esprehn@chromium.org
BUG=526577
Committed: https://crrev.com/acdd7ea3567e0efaf8d9f94b66833770c4bdf4da
Cr-Commit-Position: refs/heads/master@{#351478}

[esprehn, 2015-09-30 00:58:38]

lgtm

[Dan Beam, 2015-09-30 02:25:19]

The CQ bit was checked by dbeam@chromium.org

[commit-bot: I haz the power, 2015-09-30 02:25:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1376463003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1376463003/1

[commit-bot: I haz the power, 2015-09-30 03:05:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-30 03:06:37]

Patchset 1 (id:??) landed as
https://crrev.com/acdd7ea3567e0efaf8d9f94b66833770c4bdf4da
Cr-Commit-Position: refs/heads/master@{#351478}