Fix position:sticky location bug when scroller is not a stacking context

Fix position:sticky location bug when scroller is not a stacking context

This was broken in http://crrev.com/e481938 when I added code to correct
for scroll offset in intermediate layers - that logic is invalid if we
arent a LayerTree descendent of the scroller.

The reason that we didn't spot that this was broken is that we keep
using will-change:transform to force-enable compositing of elements, but
this also creates a stacking context. For now I have switched this to
backface-visibility:hidden, which isn't perfect but at least doesn't
create a stacking context.

BUG=699137, 706455
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2765503003
Cr-Commit-Position: refs/heads/master@{#459546}
(cherry picked from commit d5514f08a923485a8ef2a58cab355893d0e55fcb)

Review-Url: https://codereview.chromium.org/2803593007 .
Cr-Commit-Position: refs/branch-heads/3029@{#609}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed: https://chromium.googlesource.com/chromium/src/+/13a8712c4430293f11cca14eb50eaca5fd640dec

[flackr, 2017-04-06 18:42:23]

Description was changed from

==========
Fix position:sticky location bug when scroller is not a stacking context

This was broken in http://crrev.com/e481938 when I added code to correct
for scroll offset in intermediate layers - that logic is invalid if we
arent a LayerTree descendent of the scroller.

The reason that we didn't spot that this was broken is that we keep
using will-change:transform to force-enable compositing of elements, but
this also creates a stacking context. For now I have switched this to
backface-visibility:hidden, which isn't perfect but at least doesn't
create a stacking context.

BUG=699137
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2765503003
Cr-Commit-Position: refs/heads/master@{#459546}
(cherry picked from commit d5514f08a923485a8ef2a58cab355893d0e55fcb)
==========

to

==========
Fix position:sticky location bug when scroller is not a stacking context

This was broken in http://crrev.com/e481938 when I added code to correct
for scroll offset in intermediate layers - that logic is invalid if we
arent a LayerTree descendent of the scroller.

The reason that we didn't spot that this was broken is that we keep
using will-change:transform to force-enable compositing of elements, but
this also creates a stacking context. For now I have switched this to
backface-visibility:hidden, which isn't perfect but at least doesn't
create a stacking context.

BUG=699137,706455
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2765503003
Cr-Commit-Position: refs/heads/master@{#459546}
(cherry picked from commit d5514f08a923485a8ef2a58cab355893d0e55fcb)
==========

[flackr, 2017-04-06 18:44:45]

Description was changed from

==========
Fix position:sticky location bug when scroller is not a stacking context

This was broken in http://crrev.com/e481938 when I added code to correct
for scroll offset in intermediate layers - that logic is invalid if we
arent a LayerTree descendent of the scroller.

The reason that we didn't spot that this was broken is that we keep
using will-change:transform to force-enable compositing of elements, but
this also creates a stacking context. For now I have switched this to
backface-visibility:hidden, which isn't perfect but at least doesn't
create a stacking context.

BUG=699137,706455
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2765503003
Cr-Commit-Position: refs/heads/master@{#459546}
(cherry picked from commit d5514f08a923485a8ef2a58cab355893d0e55fcb)
==========

to

==========
Fix position:sticky location bug when scroller is not a stacking context

This was broken in http://crrev.com/e481938 when I added code to correct
for scroll offset in intermediate layers - that logic is invalid if we
arent a LayerTree descendent of the scroller.

The reason that we didn't spot that this was broken is that we keep
using will-change:transform to force-enable compositing of elements, but
this also creates a stacking context. For now I have switched this to
backface-visibility:hidden, which isn't perfect but at least doesn't
create a stacking context.

BUG=699137,706455
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2765503003
Cr-Commit-Position: refs/heads/master@{#459546}
(cherry picked from commit d5514f08a923485a8ef2a58cab355893d0e55fcb)

Review-Url: https://codereview.chromium.org/2803593007 .
Cr-Commit-Position: refs/branch-heads/3029@{#609}
Cr-Branched-From:
939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed:
https://chromium.googlesource.com/chromium/src/+/13a8712c4430293f11cca14eb50e...
==========

[flackr, 2017-04-06 18:44:46]

Committed patchset #1 (id:1) manually as
13a8712c4430293f11cca14eb50eaca5fd640dec.