Revert of ObjectPainter::paintAsStackingContext()

Revert of ObjectPainter::paintAsStackingContext() (patchset #4 id:80001 of https://codereview.chromium.org/1562183002/ )

Reason for revert:
Caused bug 575580

BUG=575580
Original issue's description:
> ObjectPainter::paintAsStackingContext()
> 
> Was BlockPainter::paintAsInlineBlock(). Let other places having similar
> code call the new function.
> 
> This is a preparation for further works for crbug.com/574938.
> 
> BUG=574938
> 
> Committed: https://crrev.com/3d52bb54aaa5d39147adf27e02fa04d0abd2fbf7
> Cr-Commit-Position: refs/heads/master@{#368109}

TBR=chrishtr@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=574938

[Xianzhu, 2016-01-09 00:05:01]

Created Revert of ObjectPainter::paintAsStackingContext()

[commit-bot: I haz the power, 2016-01-09 00:07:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1569293003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1569293003/1

[Xianzhu, 2016-01-09 00:08:20]

The CQ bit was unchecked by wangxianzhu@chromium.org