[css-contain] Make contain:layout a stacking context

The CSSWG has recently resolved that layout containment
should create a stacking context like paint containment
(see issue https://github.com/w3c/csswg-drafts/issues/2942).

This is the spec text about this
(https://drafts.csswg.org/css-contain/#containment-layout):
  "5. The element creates a stacking context."

The patch is just a simple change in
ComputedStyle::UpdateIsStackingContext() to add the new condition.

Apart from that TestExpectations file is updated
as we're now passing some tests from WPT.
We're also failing one test, but for an unrelated issue
(see bug #880802).

BUG=870157
TEST=external/wpt/css/css-contain/contain-layout-016.html
TEST=external/wpt/css/css-contain/contain-layout-018.html
TEST=external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-layout-stacking-context-001.html

Change-Id: Icdc102692801534364adf3fc0929192b886cdbc4
Reviewed-on: https://chromium-review.googlesource.com/1211922
Commit-Queue: Manuel Rego <rego@igalia.com>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589689}

third_party/WebKit/LayoutTests/TestExpectations

@@ -301,10 +301,11 @@ crbug.com/174167 external/wpt/css/css-tables/visibility-collapse-rowcol-002.html
 
 # [css-contain]
 
+crbug.com/880802 external/wpt/css/css-contain/contain-layout-017.html [ Failure ]
 crbug.com/847274 external/wpt/css/css-contain/contain-paint-005.html [ Failure ]
 crbug.com/847274 external/wpt/css/css-contain/contain-paint-006.html [ Failure ]
+crbug.com/880802 external/wpt/css/css-contain/contain-paint-021.html [ Failure ]
 crbug.com/881057 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-layout-formatting-context-margin-001.html [ Failure ]
-crbug.com/881057 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-layout-stacking-context-001.html [ Failure ]
 crbug.com/881057 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-paint-clip-002.html [ Failure ]
 crbug.com/881057 [ Mac ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-paint-clip-003.html [ Failure ]
 crbug.com/881057 [ Mac ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-paint-clip-004.html [ Failure ]
@@ -2887,8 +2888,6 @@ crbug.com/626703 external/wpt/css/css-contain/contain-layout-cell-002.html [ Fai
 crbug.com/626703 external/wpt/css/css-contain/contain-paint-clip-015.html [ Failure ]
 crbug.com/626703 external/wpt/css/css-contain/contain-size-monolithic-001.html [ Failure ]
 crbug.com/626703 external/wpt/css/css-contain/contain-style-counters-004.html [ Failure ]
-crbug.com/868102 external/wpt/css/css-contain/contain-paint-021.html [ Failure ]
-crbug.com/870157 external/wpt/css/css-contain/contain-layout-016.html [ Failure ]
 crbug.com/626703 external/wpt/clear-site-data/executionContexts.sub.html [ Timeout ]
 crbug.com/626703 [ Win10 ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-column-row-gap-004.html [ Failure ]
 crbug.com/626703 [ Linux Mac Win7 ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-column-row-gap-004.html [ Failure ]

third_party/blink/renderer/core/style/computed_style.cc

@@ -932,7 +932,7 @@ void ComputedStyle::UpdateIsStackingContext(bool is_document_element,
       HasBlendMode() || HasIsolation() || HasViewportConstrainedPosition() ||
       GetPosition() == EPosition::kSticky ||
       HasPropertyThatCreatesStackingContext(WillChangeProperties()) ||
-      ContainsPaint()) {
+      ContainsPaint() || ContainsLayout()) {
     SetIsStackingContext(true);
   }
 }

third_party/blink/renderer/core/style/computed_style_test.cc

@@ -93,6 +93,14 @@ TEST(ComputedStyleTest, Preserve3dForceStackingContext) {
   EXPECT_TRUE(style->IsStackingContext());
 }
 
+TEST(ComputedStyleTest, LayoutContainmentStackingContext) {
+  scoped_refptr<ComputedStyle> style = ComputedStyle::Create();
+  EXPECT_FALSE(style->IsStackingContext());
+  style->SetContain(kContainsLayout);
+  style->UpdateIsStackingContext(false, false, false);
+  EXPECT_TRUE(style->IsStackingContext());
+}
+
 TEST(ComputedStyleTest, FirstPublicPseudoStyle) {
   scoped_refptr<ComputedStyle> style = ComputedStyle::Create();
   style->SetHasPseudoStyle(kPseudoIdFirstLine);