Set m_{width,height}AvailableToChildrenChanged when scrollbars appear

Set m_{width,height}AvailableToChildrenChanged when scrollbars appear

This is a regression from https://codereview.chromium.org/1734203002. Before
that change, we'd just call layoutBlock(true). However, the new approach
just marks for layout and eventually recurses down, so to ensure that
the children get laid out, we have to set
m_{width,height}AvailableToChildrenChanged.

BUG=594465, 593593, 590683, 593624, 593593
Review URL: https://codereview.chromium.org/1811753003

Cr-Commit-Position: refs/heads/master@{#382074}
(cherry picked from commit fbb25cec59deb052604d63036f1c5baf6efd2a5c)

Committed: https://chromium.googlesource.com/chromium/src/+/7f4a99dd2428b2395fff7db0330a4c9280054162

[cbiesinger, 2016-03-21 20:08:22]

Description was changed from

==========
Set m_{width,height}AvailableToChildrenChanged when scrollbars appear

This is a regression from https://codereview.chromium.org/1734203002. Before
that change, we'd just call layoutBlock(true). However, the new approach
just marks for layout and eventually recurses down, so to ensure that
the children get laid out, we have to set
m_{width,height}AvailableToChildrenChanged.

BUG=594465,593593,590683,593624,593593

Review URL: https://codereview.chromium.org/1811753003

Cr-Commit-Position: refs/heads/master@{#382074}
(cherry picked from commit fbb25cec59deb052604d63036f1c5baf6efd2a5c)
==========

to

==========
Set m_{width,height}AvailableToChildrenChanged when scrollbars appear

This is a regression from https://codereview.chromium.org/1734203002. Before
that change, we'd just call layoutBlock(true). However, the new approach
just marks for layout and eventually recurses down, so to ensure that
the children get laid out, we have to set
m_{width,height}AvailableToChildrenChanged.

BUG=594465,593593,590683,593624,593593

Review URL: https://codereview.chromium.org/1811753003

Cr-Commit-Position: refs/heads/master@{#382074}
(cherry picked from commit fbb25cec59deb052604d63036f1c5baf6efd2a5c)

Committed:
https://chromium.googlesource.com/chromium/src/+/7f4a99dd2428b2395fff7db0330a...
==========

[cbiesinger, 2016-03-21 20:08:23]

Committed patchset #1 (id:1) manually as
7f4a99dd2428b2395fff7db0330a4c9280054162.