[New Multicolumn] A renderer can't be both a parent and a sibling of another renderer.

[New Multicolumn] A renderer can't be both a parent and a sibling of another renderer.

In addChild(), beforeChild needs to be a descendant of the parent
that's attempting to insert a renderer.

When redirecting renderer insertion to a child
RenderMultiColumnFlowThread, update beforeChild if it's set to said
RenderMultiColumnFlowThread as well.

BUG=358597
R=leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=183315

[mstensho (USE GERRIT), 2014-09-11 13:18:40]

mstensho@opera.com changed reviewers:
+ dsinclair@chromium.org

[mstensho (USE GERRIT), 2014-09-25 06:31:50]

mstensho@opera.com changed reviewers:
+ jchaffraix@chromium.org

[mstensho (USE GERRIT), 2014-09-25 06:31:50]

I'm aware of https://code.google.com/p/chromium/issues/detail?id=417556 , but
I'm not sure if we should wait for that, since this is a crasher?

[leviw_travelin_and_unemployed, 2014-10-06 18:17:23]

Okay. LGTM.

[mstensho (USE GERRIT), 2014-10-06 19:18:24]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2014-10-06 19:19:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/568443002/1

[commit-bot: I haz the power, 2014-10-06 21:08:22]

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

[commit-bot: I haz the power, 2014-10-06 21:08:23]

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...)

[mstensho (USE GERRIT), 2014-10-06 21:15:05]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2014-10-06 21:16:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/568443002/1

[commit-bot: I haz the power, 2014-10-06 21:26:08]

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

[commit-bot: I haz the power, 2014-10-06 21:26:09]

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...)

[mstensho (USE GERRIT), 2014-10-07 07:16:09]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2014-10-07 07:16:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/568443002/1

[commit-bot: I haz the power, 2014-10-07 08:20:18]

Committed patchset #1 (id:1) as 183315