Fix animation of auto for -webkit-column-count and -webkit-column-width

Fix animation of auto for -webkit-column-count and -webkit-column-width

The CSSAnimatableValueFactory did not support the auto keyword for
-webkit-column-count or -webkit-column-width.
This patch adds support for auto being animated with these properties.

BUG=498063
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197469

[alancutter (OOO until 2018), 2015-06-09 01:18:20]

alancutter@chromium.org changed reviewers:
+ samli@chromium.org

[alancutter (OOO until 2018), 2015-06-19 04:31:45]

samli: Poke.

https://codereview.chromium.org/1169003002/diff/1/LayoutTests/animations/inte...
File LayoutTests/animations/interpolation/webkit-column-count-interpolation.html
(right):

https://codereview.chromium.org/1169003002/diff/1/LayoutTests/animations/inte...
LayoutTests/animations/interpolation/webkit-column-count-interpolation.html:49:
from: '1',
0 is not a valid value here.

[dstockwell, 2015-06-19 05:03:02]

dstockwell@chromium.org changed reviewers:
+ dstockwell@chromium.org

[dstockwell, 2015-06-19 05:03:02]

lgtm

[alancutter (OOO until 2018), 2015-06-19 06:20:46]

The CQ bit was checked by alancutter@chromium.org

[commit-bot: I haz the power, 2015-06-19 06:21:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1169003002/1

[commit-bot: I haz the power, 2015-06-19 09:24:01]

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

[commit-bot: I haz the power, 2015-06-19 09:24:02]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/67402)

[alancutter (OOO until 2018), 2015-06-19 12:36:14]

The CQ bit was checked by alancutter@chromium.org

[commit-bot: I haz the power, 2015-06-19 12:36:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1169003002/1

[commit-bot: I haz the power, 2015-06-19 13:26:17]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197469