[CSS Grid Layout] grid-template-areas should accept none value

[CSS Grid Layout] grid-template-areas should accept none value

Default value for grid-template-areas property is "none":
http://dev.w3.org/csswg/css-grid/#propdef-grid-template-areas

Currently if you set the property to "none" from JavaScript, the value
doesn't get reseted and it keeps the old value.

This patch adds support to parse it successfully and updates the test
adding the new case.

TEST=fast/css-grid-layout/grid-template-areas-get-set.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=194926

[Manuel Rego, 2015-05-05 09:30:13]

rego@igalia.com changed reviewers:
+ dsinclair@chromium.org, jchaffraix@chromium.org, leviw@chromium.org

[svillar, 2015-05-05 09:33:30]

svillar@igalia.com changed reviewers:
+ svillar@igalia.com

[svillar, 2015-05-05 09:33:30]

Informal lgtm

[dsinclair, 2015-05-05 14:28:08]

The CQ bit was checked by dsinclair@chromium.org

[dsinclair, 2015-05-05 14:28:09]

lgtm

[commit-bot: I haz the power, 2015-05-05 14:28:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1117123005/1

[commit-bot: I haz the power, 2015-05-05 16:23:00]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=194926