Unreviewed, revert [257194@main] Support ::backdrop renderer on all e…

…lements

https://bugs.webkit.org/show_bug.cgi?id=248456
rdar://102748281

Manually reverting this patch since commit-queue does not process it in https://bugs.webkit.org/show_bug.cgi?id=248640.

* Source/WebCore/css/dialog.css:
(::backdrop):
* Source/WebCore/css/html.css:
(::backdrop): Deleted.
* Source/WebCore/rendering/updating/RenderTreeUpdaterGeneratedContent.cpp:
(WebCore::RenderTreeUpdater::GeneratedContent::updateBackdropRenderer):

Canonical link: https://commits.webkit.org/257263@main

Source/WebCore/css/dialog.css

@@ -29,3 +29,12 @@ dialog:modal {
 dialog::backdrop {
     background: rgba(0, 0, 0, 0.1);
 }
+
+::backdrop {
+    display: block;
+    position: fixed;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+}

Source/WebCore/css/html.css

@@ -112,14 +112,6 @@ abbr[title], acronym[title] {
     text-decoration: dotted underline;
 }
 
-/* ::backdrop */
-
-::backdrop {
-    display: block;
-    position: fixed;
-    inset: 0;
-}
-
 /* media elements */
 
 body:-webkit-full-page-media {

Source/WebCore/rendering/updating/RenderTreeUpdaterGeneratedContent.cpp

@@ -175,6 +175,8 @@ void RenderTreeUpdater::GeneratedContent::updatePseudoElement(Element& current,
 
 void RenderTreeUpdater::GeneratedContent::updateBackdropRenderer(RenderElement& renderer)
 {
+    if (!renderer.canHaveGeneratedChildren())
+        return;
     // ::backdrop does not inherit style, hence using the view style as parent style
     auto style = renderer.getCachedPseudoStyle(PseudoId::Backdrop, &renderer.view().style());
 
@@ -192,10 +194,7 @@ void RenderTreeUpdater::GeneratedContent::updateBackdropRenderer(RenderElement&
         auto newBackdropRenderer = WebCore::createRenderer<RenderBlockFlow>(renderer.document(), WTFMove(newStyle));
         newBackdropRenderer->initializeStyle();
         renderer.setBackdropRenderer(*newBackdropRenderer.get());
-
-        // Use the renderer as parent when we can for hit-testing purposes.
-        RenderElement& parentRenderer = renderer.canHaveGeneratedChildren() ? renderer : renderer.view();
-        m_updater.m_builder.attach(parentRenderer, WTFMove(newBackdropRenderer), parentRenderer.lastChild());
+        m_updater.m_builder.attach(renderer, WTFMove(newBackdropRenderer), renderer.firstChild());
     }
 }