ComputedStyle is correct here so moving to Layout for triage

Able to reproduce this issue on reported version 64.0.3268.0  and on latest canary 64.0.3271.0 using Mac 10.12.6, Windows 10 and Ubuntu 14.04 with steps mentioned in comment#0. i.e; Content doesn't become opaque and fixed descendant is positioned to outer of the element.

This issue is seen from M50. [50.0.2661.0]. Hence considering this issue as Non-regression and marking as Untriaged.

NOTE: Issue is seen in Firefox as well.

"opaque" is not talking about the color; it is just used in the sense that follows in the next part of the sentence: "This ensures that the containing element is totally opaque for layout purposes; nothing outside can affect its internal layout, and vice versa."

The containing block aspect is a more recent change (https://github.com/w3c/csswg-drafts/commit/e25416007e6ce7f2fc87854cb42fe953b290c71a), it looks like we don't implement that yet. Marking as available for that.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bff3225e24a51702b9dd412db44a3144316ff075

commit bff3225e24a51702b9dd412db44a3144316ff075
Author: Manuel Rego Casasnovas <rego@igalia.com>
Date: Wed May 16 12:01:24 2018

[css-contain] Layout containment abspos and fixed descendants

An element with "contain: layout" should be the containing block
of any absolutely or fixed positioned descendants.

The spec is very clear regarding this
(https://drafts.csswg.org/css-contain/#containment-layout):
"The element acts as a containing block for absolutely positioned
 and fixed positioned descendants."

The patch just adds a new condition to
ComputedStyle::CanContainFixedPositionObjects().

We already had the condition for paint containment before,
so this takes advantage to add WPT tests to verify that case too.

This patch causes that contain-layout-005.html starts to fail,
but that's because of  crbug.com/843329 .
There are more failing tests related to that bug, so TestExpectations
is modified to reference it.

BUG= 785212 
TEST=external/wpt/css/css-contain/contain-layout-006.html
TEST=external/wpt/css/css-contain/contain-layout-007.html

Change-Id: I8bb1d637bd7742961a414a5007b8ee8a8d3e66ea
Reviewed-on: https://chromium-review.googlesource.com/1059557
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Manuel Rego Casasnovas <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#559045}
[modify] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/WebKit/LayoutTests/external/wpt/css/css-contain/contain-layout-006.html
[add] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/WebKit/LayoutTests/external/wpt/css/css-contain/contain-layout-007.html
[add] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/WebKit/LayoutTests/external/wpt/css/css-contain/contain-paint-009.html
[add] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/WebKit/LayoutTests/external/wpt/css/css-contain/contain-paint-010.html
[modify] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/WebKit/LayoutTests/fast/dom/Element/offset-parent-contain.html
[modify] https://crrev.com/bff3225e24a51702b9dd412db44a3144316ff075/third_party/blink/renderer/core/style/computed_style.h

The issue related to abspos or fixed elements should be fixed now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1ccccf2277af4c7bf162ac01d2674fc888b6b5c9

commit 1ccccf2277af4c7bf162ac01d2674fc888b6b5c9
Author: Manuel Rego Casasnovas <rego@igalia.com>
Date: Fri May 18 22:46:06 2018

[css-contain] Revert r559045 that broke YouTube on mobile

This is a revert of https://chromium-review.googlesource.com/1059557,
but we still keep the tests as they are right according to the spec.

We're reverting this as the branch point for M68 is very close,
we'll re-evaluate what to do once the branch is done.

BUG= 785212 ,843900,843905
TBR=mstensho@chromium.org,eae@chromium.org

Change-Id: I0d8faffe06ebd7f930daccf9dc17a412d9bcc40d
Reviewed-on: https://chromium-review.googlesource.com/1065680
Reviewed-by: Manuel Rego Casasnovas <rego@igalia.com>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Manuel Rego Casasnovas <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#560082}
[modify] https://crrev.com/1ccccf2277af4c7bf162ac01d2674fc888b6b5c9/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/1ccccf2277af4c7bf162ac01d2674fc888b6b5c9/third_party/WebKit/LayoutTests/fast/dom/Element/offset-parent-contain-expected.txt
[modify] https://crrev.com/1ccccf2277af4c7bf162ac01d2674fc888b6b5c9/third_party/blink/renderer/core/style/computed_style.h

Reopening this, as it was needed to revert the change,
as it broke YouTube on mobile.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/10def17fd2d6c1e0c72c812e897c73eea1bd6bcd

commit 10def17fd2d6c1e0c72c812e897c73eea1bd6bcd
Author: Manuel Rego Casasnovas <rego@igalia.com>
Date: Tue May 22 21:41:42 2018

[css-contain] Use counter for layout containment positioned descendants

The patch to fix  crbug.com/785212  broke some sites,
it was making "contain: layout" elements to behave as containing blocks
for absolutely and fixed positioned descendants.

To check how many websites are affected by this, we're adding
a use counter in this patch.

BUG= 785212 

Change-Id: I35ea1f58a4e7570543c911607c1e6b81bc401ea8
Reviewed-on: https://chromium-review.googlesource.com/1067917
Commit-Queue: Manuel Rego Casasnovas <rego@igalia.com>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560789}
[modify] https://crrev.com/10def17fd2d6c1e0c72c812e897c73eea1bd6bcd/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/10def17fd2d6c1e0c72c812e897c73eea1bd6bcd/third_party/blink/renderer/core/frame/use_counter_test.cc
[modify] https://crrev.com/10def17fd2d6c1e0c72c812e897c73eea1bd6bcd/third_party/blink/renderer/core/layout/layout_object.cc
[modify] https://crrev.com/10def17fd2d6c1e0c72c812e897c73eea1bd6bcd/tools/metrics/histograms/enums.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/db71b93784806ce5e46bdadd494c472858f21d43

commit db71b93784806ce5e46bdadd494c472858f21d43
Author: Manuel Rego Casasnovas <rego@igalia.com>
Date: Fri Jul 20 23:26:47 2018

[css-contain] Layout containment abspos and fixed descendants

An element with "contain: layout" should be the containing block
of any absolutely or fixed positioned descendants.

The spec is very clear regarding this
(https://drafts.csswg.org/css-contain/#containment-layout):
"The element acts as a containing block for absolutely positioned
 and fixed positioned descendants."

This was already implemented in r559045 but it was reverted
temporary as some sites (like YouTube on mobile) got broken.
For that reason we added a use counter, that is now in lower numbers
since YouTube has been updated to follow the new behavior.

The WPT test suite already has tests covering this,
so this patch just removes them from TestExpectations file.

BUG= 785212 

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I381af403bba1b6976e88ac02a462b28c424aa3af
Reviewed-on: https://chromium-review.googlesource.com/1144939
Commit-Queue: Manuel Rego <rego@igalia.com>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577030}
[modify] https://crrev.com/db71b93784806ce5e46bdadd494c472858f21d43/third_party/WebKit/LayoutTests/TestExpectations
[delete] https://crrev.com/025c4917a3d0a3420ec520807c348741988102ac/third_party/WebKit/LayoutTests/fast/dom/Element/offset-parent-contain-expected.txt
[modify] https://crrev.com/db71b93784806ce5e46bdadd494c472858f21d43/third_party/blink/renderer/core/layout/layout_block.cc
[modify] https://crrev.com/db71b93784806ce5e46bdadd494c472858f21d43/third_party/blink/renderer/core/layout/layout_object.cc
[modify] https://crrev.com/db71b93784806ce5e46bdadd494c472858f21d43/third_party/blink/renderer/core/layout/layout_table_box_component.cc
[modify] https://crrev.com/db71b93784806ce5e46bdadd494c472858f21d43/third_party/blink/renderer/core/layout/ng/inline/ng_inline_item.cc

Note this current open issue on the spec, which is distinct from this, but related:
https://github.com/w3c/csswg-drafts/issues/2942

Regarding last comment by Florian, we'll report a new bug once that's on the spec.
Apart from that we found issues related to paint containment and stacking contexts:
https://bugs.chromium.org/p/chromium/issues/detail?id=868102

This issue is now fixed.

 Issue 869279  has been merged into this issue.