Add srcset negative x descriptor value tests

Add srcset negative x descriptor value tests

The implementation handled negative x descriptors properly, but they weren't tested.

This CL fixes that.

BUG=376726
CC=simonp@opera.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175033

[zcorpan, 2014-05-23 11:22:15]

LGTM

[eseidel, 2014-05-28 23:29:50]

The CQ bit was checked by eseidel@chromium.org

[commit-bot: I haz the power, 2014-05-28 23:30:22]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/yoav@yoav.ws/292383004/1

[commit-bot: I haz the power, 2014-05-28 23:30:25]

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

[commit-bot: I haz the power, 2014-05-28 23:30:29]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[eseidel, 2014-05-28 23:43:20]

lgtm

[commit-bot: I haz the power, 2014-05-29 00:58:00]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[commit-bot: I haz the power, 2014-05-29 00:58:26]

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

[commit-bot: I haz the power, 2014-05-29 00:58:27]

Try jobs failed on following builders:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[Yoav Weiss, 2014-05-29 04:36:32]

The CQ bit was checked by yoav@yoav.ws

[commit-bot: I haz the power, 2014-05-29 04:36:55]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/yoav@yoav.ws/292383004/1

[commit-bot: I haz the power, 2014-05-29 04:37:36]

Change committed as 175033