Return "auto" for computed z-index on non-stacking-context element

Return "auto" for computed z-index on non-stacking-context element

Following https://codereview.chromium.org/2047283002 we were returning
"0" for getComputedStyle(element).zIndex for elements that were not
stacking contexts. Previously we would return "auto". Both behaviours
are incorrect.

This patch reverts the change in getComputedStyle() behaviour back
to "auto".

BUG=656681
Review-Url: https://chromiumcodereview.appspot.com/2439663002
Cr-Commit-Position: refs/heads/master@{#426690}
(cherry picked from commit 664d4716b91e01c779a77702e9f219c2744724e0)

Committed: https://chromium.googlesource.com/chromium/src/+/f22b7f69fd74027b685047b3f06dab55a0b69a04

[alancutter (OOO until 2018), 2016-10-25 00:04:05]

Description was changed from

==========
Return "auto" for computed z-index on non-stacking-context element

Following https://codereview.chromium.org/2047283002 we were returning
"0" for getComputedStyle(element).zIndex for elements that were not
stacking contexts. Previously we would return "auto". Both behaviours
are incorrect.

This patch reverts the change in getComputedStyle() behaviour back
to "auto".

BUG=656681

Review-Url: https://chromiumcodereview.appspot.com/2439663002
Cr-Commit-Position: refs/heads/master@{#426690}
(cherry picked from commit 664d4716b91e01c779a77702e9f219c2744724e0)
==========

to

==========
Return "auto" for computed z-index on non-stacking-context element

Following https://codereview.chromium.org/2047283002 we were returning
"0" for getComputedStyle(element).zIndex for elements that were not
stacking contexts. Previously we would return "auto". Both behaviours
are incorrect.

This patch reverts the change in getComputedStyle() behaviour back
to "auto".

BUG=656681

Review-Url: https://chromiumcodereview.appspot.com/2439663002
Cr-Commit-Position: refs/heads/master@{#426690}
(cherry picked from commit 664d4716b91e01c779a77702e9f219c2744724e0)

Committed:
https://chromium.googlesource.com/chromium/src/+/f22b7f69fd74027b685047b3f06d...
==========

[alancutter (OOO until 2018), 2016-10-25 00:04:09]

Committed patchset #1 (id:1) manually as
f22b7f69fd74027b685047b3f06dab55a0b69a04.