[New Multicolumn] Lay out flow thread again when multicol container height changes.

[New Multicolumn] Lay out flow thread again when multicol container height changes.

The column height may have to be adjusted when the multicol
container's height changes, so we need to descend into the
RenderMultiColumnFlow thread child of the RenderBlockFlow multicol
container when this happens.

BUG=359944
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170896

[ojan, 2014-04-04 19:01:54]

lgtm

[commit-bot: I haz the power, 2014-04-04 19:01:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mstensho@opera.com/225463002/1

[commit-bot: I haz the power, 2014-04-04 19:26:50]

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

[commit-bot: I haz the power, 2014-04-04 19:26:51]

Try jobs failed on following builders:
  tryserver.blink on blink_presubmit

[mstensho (USE GERRIT), 2014-04-04 19:42:31]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2014-04-04 19:42:33]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mstensho@opera.com/225463002/1

[commit-bot: I haz the power, 2014-04-04 20:16:22]

Change committed as 170896