Slightly upgrade caching of descendant of barren parent.

Slightly improved caching of descendant of barren parent.

Do not need walking up all the parents. Check the first parent, then call
isDescendantOfBarrenParent(), if the parent was already computed returns it,
no need to go further.

BUG=459381
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=192944

[k.czech, 2015-03-31 15:07:53]

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

[k.czech, 2015-03-31 15:09:02]

On 2015/03/31 15:07:53, k.czech wrote:

Before landing I will write a short description.

[dmazzoni, 2015-03-31 15:12:18]

lgtm

Thanks

[k.czech, 2015-04-01 07:53:28]

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

[commit-bot: I haz the power, 2015-04-01 07:53:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1050533002/1

[commit-bot: I haz the power, 2015-04-01 09:54:12]

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

[commit-bot: I haz the power, 2015-04-01 09:54:13]

Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/5...)

[k.czech, 2015-04-01 13:57:34]

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

[commit-bot: I haz the power, 2015-04-01 13:57:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1050533002/1

[commit-bot: I haz the power, 2015-04-01 15:03:54]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=192944