CSS Parser: Handle at-rules in declaration lists

CSS Parser: Handle at-rules in declaration lists

The css-syntax spec allows for at-rules in declaration lists. While we
don't currently support any instances of this (the only case I know
where this is used is in @page rules), we should still have the logic
so we can correctly perform error recovery here.

For example, ".a { @x { } left: 10px }" should still apply the left
property since the at-rule ends at the }.

http://dev.w3.org/csswg/css-syntax/#consume-list-of-declarations

BUG=330389
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=193243

[Timothy Loh, 2015-04-02 04:10:57]

timloh@chromium.org changed reviewers:
+ alancutter@chromium.org, dstockwell@chromium.org

[dstockwell, 2015-04-07 04:18:28]

lgtm

[Timothy Loh, 2015-04-07 04:20:04]

The CQ bit was checked by timloh@chromium.org

[commit-bot: I haz the power, 2015-04-07 04:20:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1053953002/20001

[commit-bot: I haz the power, 2015-04-07 05:42:43]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=193243