Make ::backdrop inherit from parent element

https://bugs.webkit.org/show_bug.cgi?id=263834

Reviewed by Tim Nguyen.

StyleTreeResolver/RenterTreeUpdate explicitly checked for ::backdrop
elements to remove their inheritance chain, per the spec at the time.
whatwg/fullscreen#124 was created to query
this and it was resolved that ::backdrop _should_ inherit.

This commit addresses the change by removing the check in
StyleTreeResolve to allow ::backdrop to inherit from its parent element,
and altering the check in RenderTreeUpdate to call renderer.style()
instead of renderer.view.style(). This aligns behaviour with the other
browsers and WPT.

* LayoutTests/TestExpectations:
* LayoutTests/imported/w3c/web-platform-tests/css/css-contain/container-queries/dialog-backdrop-create.html:
* Source/WebCore/rendering/updating/RenderTreeUpdaterGeneratedContent.cpp:
(WebCore::RenderTreeUpdater::GeneratedContent::updateBackdropRenderer):
* Source/WebCore/style/StyleTreeResolver.cpp:
(WebCore::Style::TreeResolver::makeResolutionContextForPseudoElement):

Canonical link: https://commits.webkit.org/270246@main

Author: keithamus

Diff for: LayoutTests/TestExpectations

@@ -6825,10 +6825,6 @@ webkit.org/b/263873 imported/w3c/web-platform-tests/scroll-animations/css/printi
 
 webkit.org/b/263923 animations/transition-and-animation-2.html [ Failure Pass ]
 
-# <dialog> element failures
-
-webkit.org/b/263834 imported/w3c/web-platform-tests/html/semantics/interactive-elements/the-dialog-element/backdrop-inherits.html [ ImageOnlyFailure ]
-
 # CloseWatcher related timeouts
 imported/w3c/web-platform-tests/html/semantics/interactive-elements/the-dialog-element/dialog-cancel-events.html [ Skip ]
 imported/w3c/web-platform-tests/html/semantics/interactive-elements/the-dialog-element/dialog-cancel-preventDefault.html [ Skip ]

Diff for: LayoutTests/imported/w3c/web-platform-tests/css/css-contain/container-queries/dialog-backdrop-create.html

@@ -15,6 +15,7 @@
     visibility: hidden;
   }
   dialog::backdrop {
+    visibility: visible;
     display: none;
     background-color: green;
   }

Diff for: Source/WebCore/rendering/updating/RenderTreeUpdaterGeneratedContent.cpp

@@ -200,8 +200,7 @@ void RenderTreeUpdater::GeneratedContent::updateBackdropRenderer(RenderElement&
         return;
     }
 
-    // ::backdrop does not inherit style, hence using the view style as parent style
-    auto style = renderer.getCachedPseudoStyle(PseudoId::Backdrop, &renderer.view().style());
+    auto style = renderer.getCachedPseudoStyle(PseudoId::Backdrop, &renderer.style());
     if (!style || style->display() == DisplayType::None) {
         destroyBackdropIfNeeded();
         return;

Diff for: Source/WebCore/style/StyleTreeResolver.cpp

@@ -515,9 +515,6 @@ ResolutionContext TreeResolver::makeResolutionContextForPseudoElement(const Elem
             if (auto* firstLineStyle = elementUpdate.style->getCachedPseudoStyle(PseudoId::FirstLine))
                 return firstLineStyle;
         }
-        // ::backdrop does not inherit style, hence using the view style as parent style
-        if (pseudoId == PseudoId::Backdrop)
-            return &m_document.renderView()->style();
         return elementUpdate.style.get();
     };