Fix use-afer-free in PrintContext.

Fix use-afer-free in PrintContext.

The LayoutBoxModelObject may have been deleted during a style recalc triggered
by setPrinting(), which PrintContext::begin() calls.

BUG=610979
Committed: https://crrev.com/fb04c5c901794b87adb71d361558439fb35f5d16
Cr-Commit-Position: refs/heads/master@{#393380}

[chrishtr, 2016-05-12 06:05:58]

Description was changed from

==========
none

BUG=
==========

to

==========
Fix use-afer-free in PrintContext.

The LayoutBoxModelObject may have been deleted during a style recalc triggered
by setPrinting(), which PrintContext::begin() calls.

BUG=610979
==========

[chrishtr, 2016-05-12 06:06:20]

chrishtr@chromium.org changed reviewers:
+ wangxianzhu@chromium.org

[Xianzhu, 2016-05-12 22:37:14]

The CQ bit was checked by wangxianzhu@chromium.org

[Xianzhu, 2016-05-12 22:37:15]

lgtm

[commit-bot: I haz the power, 2016-05-12 22:37:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1973743003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1973743003/1

[commit-bot: I haz the power, 2016-05-12 22:41:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-12 22:44:12]

Description was changed from

==========
Fix use-afer-free in PrintContext.

The LayoutBoxModelObject may have been deleted during a style recalc triggered
by setPrinting(), which PrintContext::begin() calls.

BUG=610979
==========

to

==========
Fix use-afer-free in PrintContext.

The LayoutBoxModelObject may have been deleted during a style recalc triggered
by setPrinting(), which PrintContext::begin() calls.

BUG=610979

Committed: https://crrev.com/fb04c5c901794b87adb71d361558439fb35f5d16
Cr-Commit-Position: refs/heads/master@{#393380}
==========

[commit-bot: I haz the power, 2016-05-12 22:44:13]

Patchset 1 (id:??) landed as
https://crrev.com/fb04c5c901794b87adb71d361558439fb35f5d16
Cr-Commit-Position: refs/heads/master@{#393380}