Fix download shelf visibility bug introduced by nullptr change.

Fix download shelf visibility bug introduced by nullptr change.

The bug caused the download shelf visibility to not be updated
correctly.

BUG=434594
Committed: https://crrev.com/53513eb643e20eff90854990a494057c1f4f6014
Cr-Commit-Position: refs/heads/master@{#305118}

[benwells, 2014-11-20 07:09:04]

benwells@chromium.org changed reviewers:
+ jamescook@chromium.org

[benwells, 2014-11-20 07:09:05]

doh.

[James Cook, 2014-11-20 16:28:53]

Doh!  :-)  LGTM

[benwells, 2014-11-20 23:09:08]

The CQ bit was checked by benwells@chromium.org

[commit-bot: I haz the power, 2014-11-20 23:10:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/740203002/1

[commit-bot: I haz the power, 2014-11-21 00:11:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-21 00:13:15]

Patchset 1 (id:??) landed as
https://crrev.com/53513eb643e20eff90854990a494057c1f4f6014
Cr-Commit-Position: refs/heads/master@{#305118}