RenderLayer::setHasVisibleContent shouldn't call dirtyZOrderLists()

[Ahmad-S792]

RenderLayer::setHasVisibleContent shouldn't call dirtyZOrderLists()
https://bugs.webkit.org/show_bug.cgi?id=250283

Reviewed by NOBODY (OOPS!).

Merge - https://src.chromium.org/viewvc/blink?view=rev&revision=175708

This patch remove FIXME and also dead code since there is no connection
between being visible and z-order lists.
There is no reason to mark the z-order list as dirty when changing visibility status.

* Source/WebCore/rendering/RenderLayer.cpp:
(RenderLayer::setHasVisibleContent): Remove 'dirtyZOrderList'

2633ede

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
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 2633ede)

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
	✅ 🛠 watch-sim

[smfr]

I think we may still need this code in WebKitLegacy. RenderLayer::collectLayers() only collects visibility:hidden layers if includeHiddenLayers is true, and that's only true when compositing is enabled. In WebKitLegacy, we enter compositing mode dynamically.