Make start page logo web contents transparent.

Make start page logo web contents transparent.

This CL makes the start page's logo WebView transparent. This means we
won't need to update the background color of the start page view any
more.

BUG=442021, 457750
Committed: https://crrev.com/55f1e5199dcc7363466ff424e2a1325c2fc9fa6f
Cr-Commit-Position: refs/heads/master@{#315937}

[calamity, 2015-02-11 03:40:31]

calamity@chromium.org changed reviewers:
+ mgiuca@chromium.org

[calamity, 2015-02-11 03:40:31]

calamity@chromium.org changed reviewers:
+ mgiuca@chromium.org

[Matt Giuca, 2015-02-12 02:04:54]

lgtm

[calamity, 2015-02-12 05:37:39]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2015-02-12 05:37:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/911373002/20001

[commit-bot: I haz the power, 2015-02-12 06:23:08]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-12 06:24:14]

Patchset 2 (id:??) landed as
https://crrev.com/55f1e5199dcc7363466ff424e2a1325c2fc9fa6f
Cr-Commit-Position: refs/heads/master@{#315937}