Adding test accessibility/table-headers.html.

Adding accessibility/table-headers.html test.

Test checks correctness of table headers at particular index.

BUG=441706
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=187791

[k.czech, 2014-12-16 19:19:46]

k.czech@samsung.com changed reviewers:
+ dmazzoni@chromium.org

[dmazzoni, 2014-12-17 01:03:31]

lgtm

[k.czech, 2014-12-30 12:58:16]

The CQ bit was checked by k.czech@samsung.com

[commit-bot: I haz the power, 2014-12-30 12:59:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/799913002/1

[commit-bot: I haz the power, 2014-12-30 13:59:18]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-12-30 13:59:19]

Try jobs failed on following builders:
  mac_blink_compile_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_compile_dbg/bu...)

[k.czech, 2014-12-30 18:29:41]

The CQ bit was checked by k.czech@samsung.com

[commit-bot: I haz the power, 2014-12-30 18:30:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/799913002/1

[commit-bot: I haz the power, 2014-12-30 21:33:00]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=187791