Corrupt tiles when scrolling and selecting text quickly.

[mattwoodrow]

77e5bb3

Corrupt tiles when scrolling and selecting text quickly.
https://bugs.webkit.org/show_bug.cgi?id=268430
<rdar://121934201>

Reviewed by Simon Fraser.

If ensureBufferForDisplay returns SwapBuffersDisplayRequirement::NeedsNoDisplay, then we don't want
to call prepareForDisplay. The latter copies pixels from the old front buffer into the new one,
and when no display is required there wasn't a front/back swap, so no copy needed.

This caused issues because we also set 'm_previouslyPaintedRect` to the (empty!) dirty area,
effectively recording that the front and back buffers were identical, despite it likely
not being true. The next attempt to paint these buffers would omit a back-to-front copy,
thinking the buffers were identical, and then we'd do a partial update on top of stale content.

This happens when scrolling, since scrolling tiles get pooled (and made volatile), then
recycled.

* LayoutTests/compositing/repaint/needs-no-display-volatile-repaint-expected.html: Added.
* LayoutTests/compositing/repaint/needs-no-display-volatile-repaint.html: Added.
* Source/WebKit/GPUProcess/graphics/RemoteRenderingBackend.cpp:
(WebKit::RemoteRenderingBackend::prepareImageBufferSetsForDisplay):
(WebKit::RemoteRenderingBackend::prepareImageBufferSetsForDisplaySync):

Canonical link: https://commits.webkit.org/273838@main

b9c1e23

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	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 4ed16d4)

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	❌ 🧪 mac-wk1	✅ 🛠 gtk
⏳ 🛠 🧪 jsc	✅ 🧪 api-ios	❌ 🧪 mac-wk2	❌ 🧪 gtk-wk2
	✅ 🛠 tv	❌ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	⏳ 🛠 tv-sim	❌ 🧪 mac-wk2-stress
	⏳ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

Starting EWS tests for b9c1e23. Live statuses available at the PR page, #23558

[webkit-early-warning-system]

EWS run on current version of this PR (hash b9c1e23)

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	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 273838@main (77e5bb3): https://commits.webkit.org/273838@main

Reviewed commits have been landed. Closing PR #23558 and removing active labels.