Fix a bug that generic thumbnail is visible behind transparent thumbnail.

Fix a bug that generic thumbnail is visible behind transparent thumbnail.

BUG=459326
TEST=open a folder which contains transparent image and confirm that generic thumbnail is not visible behind thumbnail.

Committed: https://crrev.com/1d7c9bcbdbce27fc656fda9364e00bf512795e49
Cr-Commit-Position: refs/heads/master@{#317033}

[yawano, 2015-02-19 12:02:11]

yawano@chromium.org changed reviewers:
+ fukino@chromium.org

[yawano, 2015-02-19 12:02:11]

PTAL. Thank you!

[yawano, 2015-02-19 12:24:39]

As we talked offline, I created a new patch to set background-color directly.
This could make the CL much simpler. PTAL. Thank you!

[fukino, 2015-02-19 12:25:28]

On 2015/02/19 12:24:39, yawano wrote:
> As we talked offline, I created a new patch to set background-color directly.
> This could make the CL much simpler. PTAL. Thank you!

lgtm. Thanks!

[yawano, 2015-02-19 12:25:56]

On 2015/02/19 12:25:28, fukino wrote:
> On 2015/02/19 12:24:39, yawano wrote:
> > As we talked offline, I created a new patch to set background-color
directly.
> > This could make the CL much simpler. PTAL. Thank you!
> 
> lgtm. Thanks!

Thank you!

[yawano, 2015-02-19 12:25:58]

The CQ bit was checked by yawano@chromium.org

[commit-bot: I haz the power, 2015-02-19 12:27:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/935333003/20001

[commit-bot: I haz the power, 2015-02-19 12:45:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-19 12:46:50]

Patchset 2 (id:??) landed as
https://crrev.com/1d7c9bcbdbce27fc656fda9364e00bf512795e49
Cr-Commit-Position: refs/heads/master@{#317033}