Web Inspector: Don't show ::backdrop rules for elements without a backdrop

[patrickangle]

c5064e5

Web Inspector: Don't show `::backdrop` rules for elements without a backdrop
https://bugs.webkit.org/show_bug.cgi?id=251466
rdar://104889944

Reviewed by Tim Nguyen.

`::backdrop` only applies to elements in the top layer. Like `::marker`, we should not display this selector for elements it can't apply to.

* LayoutTests/inspector/css/getMatchedStylesForNode.html:
* LayoutTests/inspector/css/getMatchedStylesForNodeBackdropPseudoId-expected.txt: Added.
* LayoutTests/inspector/css/getMatchedStylesForNodeBackdropPseudoId.html: Added.
* Source/WebCore/inspector/agents/InspectorCSSAgent.cpp:
(WebCore::InspectorCSSAgent::getMatchedStylesForNode):

Canonical link: https://commits.webkit.org/259894@main

ab7da9b

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	❌ 🛠 🧪 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🛠 gtk	✅ 🛠 wincairo
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash ab7da9b)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	❌ 🛠 🧪 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🛠 gtk	✅ 🛠 wincairo
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 259894@main (c5064e5): https://commits.webkit.org/259894@main

Reviewed commits have been landed. Closing PR #9638 and removing active labels.