Make getProperty more strict when handling the priority parameter

Make getProperty more strict when handling the priority parameter

Make getProperty more strict when handling the priority parameter. Before this patch
only a substring search on "important" was done. However CSSOM is quite clear to be more strict :

http://dev.w3.org/csswg/cssom/#dom-cssstyledeclaration-setproperty
5. If priority is not the empty string and is not an ASCII case-insensitive match for the string "important", terminate this algorithm.

This patch implements that more strict behavior and adds a test.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=167883

[rwlbuis, 2014-02-25 22:57:45]

This CL is split out from https://codereview.chromium.org/141243006/ as
requested. PTAL :)

[esprehn, 2014-02-26 01:18:57]

lgtm

[rwlbuis, 2014-02-26 01:20:13]

The CQ bit was checked by rob.buis@samsung.com

[commit-bot: I haz the power, 2014-02-26 04:41:03]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rob.buis@samsung.com/180353002/20001

[Paweł Hajdan Jr., 2014-02-26 04:41:40]

The CQ bit was unchecked by phajdan.jr@chromium.org

[Paweł Hajdan Jr., 2014-02-26 05:27:34]

The CQ bit was checked by phajdan.jr@chromium.org

[commit-bot: I haz the power, 2014-02-26 05:28:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rob.buis@samsung.com/180353002/20001

[commit-bot: I haz the power, 2014-02-26 09:59:37]

Change committed as 167883