Fix font rendering in experimental app list tiles.

Fix font rendering in experimental app list tiles.

This CL fixes font rendering for experimental app list tiles by setting
a background.

BUG=406989
Committed: https://crrev.com/6fcede3f04bcc08ce4bbafb83b7444799e9700c4
Cr-Commit-Position: refs/heads/master@{#291849}

[tapted, 2014-08-25 07:00:47]

lgtm - I think there's a bug that the text isn't falling back to a
non-subpixel-AA rendering..  but we wouldn't want that fallback anyway, and I'm
fairly certain that the only way for subpixel AA to work is by having something
painting to the canvas first, which is what this will do. So all good.

[calamity, 2014-08-26 02:38:55]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2014-08-26 02:40:19]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/calamity@chromium.org/499983002/1

[calamity, 2014-08-26 02:44:23]

Patchset #2 (id:20001) has been deleted

[calamity, 2014-08-26 03:54:30]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2014-08-26 03:56:17]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/calamity@chromium.org/499983002/1

[commit-bot: I haz the power, 2014-08-26 05:44:55]

Committed patchset #1 (1) as fe6b303bcf95c47c26eb22843d848fa8152ffe6a

[commit-bot: I haz the power, 2014-09-10 02:40:48]

Patchset 1 (id:??) landed as
https://crrev.com/6fcede3f04bcc08ce4bbafb83b7444799e9700c4
Cr-Commit-Position: refs/heads/master@{#291849}