Once the flow thread needs layout, mark all column sets for layout as well.

Once the flow thread needs layout, mark all column sets for layout as well.

We need this to make sure that overflow is updated. Laying out a column set is
very cheap anyway, since they never have children. Since we now do this, we can
remove a few setNeedsLayout calls scattered around the code.

BUG=540512
R=leviw@chromium.org

Committed: https://crrev.com/bf1899ac2a9209c1d2a970d298290f54bd91d1e3
Cr-Commit-Position: refs/heads/master@{#355568}

[leviw_travelin_and_unemployed, 2015-10-22 17:19:08]

Woot! Way better. LGTM.

[leviw_travelin_and_unemployed, 2015-10-22 17:19:11]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2015-10-22 17:20:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1414193004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1414193004/1

[commit-bot: I haz the power, 2015-10-22 17:35:14]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-22 17:35:56]

Patchset 1 (id:??) landed as
https://crrev.com/bf1899ac2a9209c1d2a970d298290f54bd91d1e3
Cr-Commit-Position: refs/heads/master@{#355568}