REGRESSION (UI-side compositing?): Sporadic failures in layout tests due to wrong test images

[smfr]

b289d5f

REGRESSION (UI-side compositing?): Sporadic failures in layout tests due to wrong test images
https://bugs.webkit.org/show_bug.cgi?id=271348
rdar://120050275

Reviewed by Tim Horton.

When we take snapshots of layout tests, we wait for a `callAfterNextPresentationUpdate()`, which
waits for a transaction to come from the web process. However, it doesn't wait for the subsequent
Core Animation commit, which actually pushes changes to WindowServer. Yet the snapshot we do is
a WindowServer snapshot (`PlatformWebView::windowSnapshotImage()`), so we can sometimes capture state that is stale.

We don't actually know when our new content gets to WindowServer and will show up in a snapshot,
but we can reduce the raciness by at least waiting for the Core Animation commit to complete.
So add `callAfterNextPresentationUpdateAndLayerCommit()` and use it `WebPageProxy::forceRepaint()`.
Also update `-[WKWebView takeSnapshotWithConfiguration:]` to use it.

* Source/WebKit/UIProcess/API/Cocoa/WKWebView.mm:
(-[WKWebView takeSnapshotWithConfiguration:completionHandler:]):
* Source/WebKit/UIProcess/Cocoa/WebPageProxyCocoa.mm:
(WebKit::WebPageProxy::callAfterNextPresentationUpdateAndLayerCommit):
* Source/WebKit/UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::forceRepaint):
(WebKit::WebPageProxy::callAfterNextPresentationUpdateAndLayerCommit):
* Source/WebKit/UIProcess/WebPageProxy.h:

Canonical link: https://commits.webkit.org/276494@main

ff16eed

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
⏳ 🧪 style	⏳ 🛠 ios	⏳ 🛠 mac	⏳ 🛠 wpe	⏳ 🛠 wincairo
⏳ 🧪 bindings	⏳ 🛠 ios-sim	⏳ 🛠 mac-AS-debug	⏳ 🧪 wpe-wk2
⏳ 🧪 webkitperl	⏳ 🧪 ios-wk2	⏳ 🧪 api-mac	⏳ 🧪 api-wpe
⏳ 🧪 webkitpy	⏳ 🧪 ios-wk2-wpt	⏳ 🧪 mac-wk1	⏳ 🛠 wpe-skia
⏳ 🛠 🧪 jsc	⏳ 🧪 api-ios	⏳ 🧪 mac-wk2	⏳ 🛠 gtk
⏳ 🛠 🧪 jsc-arm64	⏳ 🛠 tv	⏳ 🧪 mac-AS-debug-wk2	⏳ 🧪 gtk-wk2
⏳ 🧪 services	⏳ 🛠 tv-sim	⏳ 🧪 mac-wk2-stress	⏳ 🧪 api-gtk
✅ 🛠 🧪 merge	⏳ 🛠 watch		⏳ 🛠 jsc-armv7
	⏳ 🛠 watch-sim		⏳ 🧪 jsc-armv7-tests

[webkit-early-warning-system]

EWS run on current version of this PR (hash 7bca848)

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

[webkit-commit-queue]

Committed 276494@main (b289d5f): https://commits.webkit.org/276494@main

Reviewed commits have been landed. Closing PR #26214 and removing active labels.