Check null m_parent in PaintLayer::insertOnlyThisLayerAfterStyleChange()

Check null m_parent in PaintLayer::insertOnlyThisLayerAfterStyleChange()

PaintLayer::m_parent may be nullptr if an orphan LayoutObject is set
style causing it to create a layer.

The problem was only detected by ubsan_vptr because though there was
call to PaintLayer::enclosingSelfPaintingLayer() with null 'this', the
method returns null without any actual harm :)

BUG=604534
TEST=All tests pass with ubsan_vptr

Committed: https://crrev.com/c24d1e3d26bcdd4fc4afbc579ec65fbaadd4fbfa
Cr-Commit-Position: refs/heads/master@{#388286}

[Xianzhu, 2016-04-19 18:01:23]

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

[pdr., 2016-04-19 18:29:04]

LGTM

[Xianzhu, 2016-04-19 18:35:52]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2016-04-19 18:36:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1901193002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1901193002/1

[commit-bot: I haz the power, 2016-04-19 19:50:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-04-22 19:15:23]

Description was changed from

==========
Check null m_parent in PaintLayer::insertOnlyThisLayerAfterStyleChange()

PaintLayer::m_parent may be nullptr if an orphan LayoutObject is set
style causing it to create a layer.

The problem was only detected by ubsan_vptr because though there was
call to PaintLayer::enclosingSelfPaintingLayer() with null 'this', the
method returns null without any actual harm :)

BUG=604534
TEST=All tests pass with ubsan_vptr
==========

to

==========
Check null m_parent in PaintLayer::insertOnlyThisLayerAfterStyleChange()

PaintLayer::m_parent may be nullptr if an orphan LayoutObject is set
style causing it to create a layer.

The problem was only detected by ubsan_vptr because though there was
call to PaintLayer::enclosingSelfPaintingLayer() with null 'this', the
method returns null without any actual harm :)

BUG=604534
TEST=All tests pass with ubsan_vptr

Committed: https://crrev.com/c24d1e3d26bcdd4fc4afbc579ec65fbaadd4fbfa
Cr-Commit-Position: refs/heads/master@{#388286}
==========

[commit-bot: I haz the power, 2016-04-22 19:15:24]

Patchset 1 (id:??) landed as
https://crrev.com/c24d1e3d26bcdd4fc4afbc579ec65fbaadd4fbfa
Cr-Commit-Position: refs/heads/master@{#388286}