Do not enable stacking context with transform animation + some fill mode

In our previous CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1066630
We make an element containing block and enable its stacking context when
this element has transform animation with forwards or both fill-mode.
This change is breaking the stacking context behavior where inbox
depends on.

This CL keeps the containing block behavior but reverts the stacking
context. Unit tests are updated.

Bug: 899759
Change-Id: I1f519c3383df9a89bcd0c2ec9f15e1c9b8ca1dc0
Reviewed-on: https://chromium-review.googlesource.com/c/1330282Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Anders Ruud <andruud@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607336}

third_party/blink/renderer/core/animation/compositor_animations_test.cc

@@ -1929,27 +1929,22 @@ TEST_F(AnimationCompositorAnimationsTest, HasCSSAnimationsWithFillMode) {
   Element* target1 = document->getElementById("target1");
   const ComputedStyle* style1 = target1->GetLayoutObject()->Style();
   EXPECT_FALSE(style1->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_FALSE(style1->HasTransformRelatedProperty());
-  // HasOpacity is true;
-  EXPECT_TRUE(style1->IsStackingContext());
+  EXPECT_FALSE(style1->CanContainFixedPositionObjects(false));
 
   Element* target2 = document->getElementById("target2");
   const ComputedStyle* style2 = target2->GetLayoutObject()->Style();
   EXPECT_TRUE(style2->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_TRUE(style2->HasTransformRelatedProperty());
-  EXPECT_TRUE(style2->IsStackingContext());
+  EXPECT_TRUE(style2->CanContainFixedPositionObjects(false));
 
   Element* target3 = document->getElementById("target3");
   const ComputedStyle* style3 = target3->GetLayoutObject()->Style();
   EXPECT_TRUE(style3->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_TRUE(style3->HasTransformRelatedProperty());
-  EXPECT_TRUE(style3->IsStackingContext());
+  EXPECT_TRUE(style3->CanContainFixedPositionObjects(false));
 
   Element* target4 = document->getElementById("target4");
   const ComputedStyle* style4 = target4->GetLayoutObject()->Style();
   EXPECT_FALSE(style4->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_FALSE(style4->HasTransformRelatedProperty());
-  EXPECT_TRUE(style4->IsStackingContext());
+  EXPECT_FALSE(style4->CanContainFixedPositionObjects(false));
 }
 
 TEST_F(AnimationCompositorAnimationsTest, HasWebAnimationsWithFillMode) {
@@ -1958,27 +1953,22 @@ TEST_F(AnimationCompositorAnimationsTest, HasWebAnimationsWithFillMode) {
   Element* target1 = document->getElementById("target1");
   const ComputedStyle* style1 = target1->GetLayoutObject()->Style();
   EXPECT_FALSE(style1->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_FALSE(style1->HasTransformRelatedProperty());
-  // HasOpacity is true;
-  EXPECT_TRUE(style1->IsStackingContext());
+  EXPECT_FALSE(style1->CanContainFixedPositionObjects(false));
 
   Element* target2 = document->getElementById("target2");
   const ComputedStyle* style2 = target2->GetLayoutObject()->Style();
   EXPECT_TRUE(style2->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_TRUE(style2->HasTransformRelatedProperty());
-  EXPECT_TRUE(style2->IsStackingContext());
+  EXPECT_TRUE(style2->CanContainFixedPositionObjects(false));
 
   Element* target3 = document->getElementById("target3");
   const ComputedStyle* style3 = target3->GetLayoutObject()->Style();
   EXPECT_TRUE(style3->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_TRUE(style3->HasTransformRelatedProperty());
-  EXPECT_TRUE(style3->IsStackingContext());
+  EXPECT_TRUE(style3->CanContainFixedPositionObjects(false));
 
   Element* target4 = document->getElementById("target4");
   const ComputedStyle* style4 = target4->GetLayoutObject()->Style();
   EXPECT_FALSE(style4->HasTransformAnimationWithForwardsOrBothFillMode());
-  EXPECT_FALSE(style4->HasTransformRelatedProperty());
-  EXPECT_TRUE(style4->IsStackingContext());
+  EXPECT_FALSE(style4->CanContainFixedPositionObjects(false));
 }
 
 }  // namespace blink

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

@@ -2074,10 +2074,9 @@ class ComputedStyle : public ComputedStyleBase,
   // will-change:transform should result in the same rendering behavior as
   // having a transform, including the creation of a containing block for fixed
   // position descendants.
-  CORE_EXPORT bool HasTransformRelatedProperty() const {
+  bool HasTransformRelatedProperty() const {
     return HasTransform() || Preserves3D() || HasPerspective() ||
-           HasWillChangeTransformHint() ||
-           HasTransformAnimationWithForwardsOrBothFillMode();
+           HasWillChangeTransformHint();
   }
 
   // Paint utility functions.
@@ -2124,6 +2123,7 @@ class ComputedStyle : public ComputedStyleBase,
   }
   bool CanContainFixedPositionObjects(bool is_document_element) const {
     return HasTransformRelatedProperty() ||
+           HasTransformAnimationWithForwardsOrBothFillMode() ||
            // Filter establishes containing block for non-document elements:
            // https://drafts.fxtf.org/filter-effects-1/#FilterProperty
            (!is_document_element && HasFilter());