[view-transitions] Names should be tree-scoped

https://bugs.webkit.org/show_bug.cgi?id=273883
rdar://127995859

Reviewed by Antti Koivisto.

Corresponding spec issue: w3c/csswg-drafts#10145
Corresponding spec PR: w3c/csswg-drafts#10306

This ignores view-transition names from shadow DOM, given the pseudo-elements are linked to the document element,
exposing shadow DOM names to the view transition pseudo-elements would be a violation of shadow DOM principles.

We don't check for the tree scope directly in `forEachRendererInPaintOrder` because a shadow DOM element might have
flat tree descendants that have an outer tree scope.

We also use the `Styleable`'s element instead of `RenderElement`'s element because for pseudo-elements we want to consider
the associated element's tree scope.

* LayoutTests/TestExpectations:
* LayoutTests/platform/glib/TestExpectations:
* Source/WebCore/dom/ViewTransition.cpp:
(WebCore::ViewTransition::captureOldState):
(WebCore::ViewTransition::captureNewState):

Canonical link: https://commits.webkit.org/278704@main

LayoutTests/TestExpectations

@@ -6929,7 +6929,6 @@ imported/w3c/web-platform-tests/css/css-view-transitions/snapshot-containing-blo
 imported/w3c/web-platform-tests/css/css-view-transitions/fractional-translation-from-position.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/scroller-child.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/scroller.html [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/css/css-view-transitions/names-are-tree-scoped.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/iframe-and-main-frame-transition-new-main-new-iframe.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/iframe-and-main-frame-transition-old-main-new-iframe.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/iframe-and-main-frame-transition-old-main-old-iframe.html [ ImageOnlyFailure ]

LayoutTests/platform/glib/TestExpectations

@@ -4145,6 +4145,7 @@ imported/w3c/web-platform-tests/css/css-view-transitions/massive-element-on-top-
 imported/w3c/web-platform-tests/css/css-view-transitions/massive-element-right-of-viewport-offscreen-old.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/massive-element-below-viewport-offscreen-old.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/massive-element-left-of-viewport-offscreen-old.html [ ImageOnlyFailure ]
+imported/w3c/web-platform-tests/css/css-view-transitions/names-are-tree-scoped.html [ ImageOnlyFailure ]
 
 imported/w3c/web-platform-tests/svg/text/reftests/transform-dynamic-change.html [ ImageOnlyFailure ]
 

Source/WebCore/dom/ViewTransition.cpp

@@ -349,7 +349,8 @@ ExceptionOr<void> ViewTransition::captureOldState()
         m_initialLargeViewportSize = view->sizeForCSSLargeViewportUnits();
 
         auto result = forEachRendererInPaintOrder([&](RenderLayerModelObject& renderer) -> ExceptionOr<void> {
-            if (!Styleable::fromRenderer(renderer))
+            auto styleable = Styleable::fromRenderer(renderer);
+            if (!styleable || &styleable->element.treeScope() != document())
                 return { };
 
             if (auto name = effectiveViewTransitionName(renderer); !name.isNull()) {
@@ -394,8 +395,8 @@ ExceptionOr<void> ViewTransition::captureNewState()
     ListHashSet<AtomString> usedTransitionNames;
     if (CheckedPtr view = document()->renderView()) {
         auto result = forEachRendererInPaintOrder([&](RenderLayerModelObject& renderer) -> ExceptionOr<void> {
-            std::optional<const Styleable> styleable = Styleable::fromRenderer(renderer);
-            if (!styleable)
+            auto styleable = Styleable::fromRenderer(renderer);
+            if (!styleable || &styleable->element.treeScope() != document())
                 return { };
 
             if (auto name = effectiveViewTransitionName(renderer); !name.isNull()) {