AX: Some places in accessibility traverse through VisiblePositions without checking progress was made, meaning we can loop forever

[twilco]

57b2f8d

AX: Some places in accessibility traverse through VisiblePositions without checking progress was made, meaning we can loop forever
https://bugs.webkit.org/show_bug.cgi?id=312932
rdar://175280603

Reviewed by Joshua Hoffman.

In 311153@main we fixed three while-loops in AccessibilityObject.cpp where
VisiblePosition::next() or previous() could return the same position, causing
an infinite loop and permanently hanging the main-thread. This change applies
the same defensive pattern to five additional loops that have the same vulnerability:

1. leftLineVisiblePositionRange: previous() loop without progress check
2. rightLineVisiblePositionRange: next() loop without progress check
3. updateAXLineStartForVisiblePosition: while(true) with previous() and no
 stuck-position guard
4. characterOffsetFromVisiblePosition: nextVisuallyDistinctCandidate loop
 with no guard despite comments acknowledging the risk
5. characterOffsetForBounds: bidirectional CharacterOffset iteration with no
 stuck-position check

* LayoutTests/accessibility/left-right-line-range-display-table-in-flex-expected.txt: Added.
* LayoutTests/accessibility/left-right-line-range-display-table-in-flex.html: Added.
* LayoutTests/platform/glib/TestExpectations:
* Source/WebCore/accessibility/AXObjectCache.cpp:
(WebCore::AXObjectCache::characterOffsetFromVisiblePosition):
(WebCore::AXObjectCache::characterOffsetForBounds):
* Source/WebCore/accessibility/AccessibilityObject.cpp:
(WebCore::updateAXLineStartForVisiblePosition):
(WebCore::AccessibilityObject::leftLineVisiblePositionRange const):
(WebCore::AccessibilityObject::rightLineVisiblePositionRange const):

Canonical link: https://commits.webkit.org/311749@main

e3ff0ef

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash e3ff0ef)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 311749@main (57b2f8d): https://commits.webkit.org/311749@main

Reviewed commits have been landed. Closing PR #63268 and removing active labels.