The following layout tests are flakey crashes on Apple Mojave Debug WK1 (Tests): accessibility/mac/search-text/search-text.html <https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=accessibility%2Fmac%2Fsearch-text%2Fsearch-text.html> accessibility/mac/select-text/select-text-1.html <https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&revision=254433&tests=accessibility%2Fmac%2Fselect-text%2Fselect-text-1.html> Example test run: <https://build.webkit.org/builders/Apple%20Mojave%20Debug%20WK1%20(Tests)/builds/7970> Example test results: <https://build.webkit.org/results/Apple%20Mojave%20Debug%20WK1%20(Tests)/r254433%20(7970)/results.html> This crash is the same assertion as this bug, but seems to have a different cause (and different stack trace): Bug 204933: REGRESSION: ASSERTION FAILED: FontCache::singleton().generation() == m_generation Assertion failure: ASSERTION FAILED: FontCache::singleton().generation() == m_generation ./platform/graphics/FontCascadeFonts.cpp(180) : const WebCore::FontRanges &WebCore::FontCascadeFonts::realizeFallbackRangesAt(const WebCore::FontCascadeDescription &, unsigned int) 1 0x115928659 WTFCrash 2 0x126a72f8b WTFCrashWithInfo(int, char const*, char const*, int) 3 0x12a30617d WebCore::FontCascadeFonts::realizeFallbackRangesAt(WebCore::FontCascadeDescription const&, unsigned int) 4 0x126c12101 WebCore::FontCascadeFonts::primaryFont(WebCore::FontCascadeDescription const&) 5 0x126c0c1e4 WebCore::FontCascade::primaryFont() const 6 0x1298bc475 WebCore::FontCascade::fontMetrics() const 7 0x12aae5a55 WebCore::RenderStyle::fontMetrics() const 8 0x128fee241 WebCore::CSSPrimitiveValue::equalForLengthResolution(WebCore::RenderStyle const&, WebCore::RenderStyle const&) 9 0x12ac10884 WebCore::Style::MatchedDeclarationsCache::Entry::isUsableAfterHighPriorityProperties(WebCore::RenderStyle const&) const 10 0x12ac5e429 WebCore::Style::Resolver::applyMatchedProperties(WebCore::Style::Resolver::State&, WebCore::Style::MatchResult const&, WebCore::Style::Resolver::UseMatchedDeclarationsCache) 11 0x12ac5cdcc WebCore::Style::Resolver::styleForElement(WebCore::Element const&, WebCore::RenderStyle const*, WebCore::RenderStyle const*, WebCore::RuleMatchingBehavior, WebCore::SelectorFilter const*) 12 0x12ac89e52 WebCore::Style::TreeResolver::styleForElement(WebCore::Element&, WebCore::RenderStyle const&) 13 0x12ac8a37b WebCore::Style::TreeResolver::resolveElement(WebCore::Element&) 14 0x12ac8be09 WebCore::Style::TreeResolver::resolveComposedTree() 15 0x12ac8cbc8 WebCore::Style::TreeResolver::resolve() 16 0x12922d34d WebCore::Document::resolveStyle(WebCore::Document::ResolveStyleType) 17 0x12922debd WebCore::Document::updateStyleIfNeeded() 18 0x129229249 WebCore::Document::updateLayout() 19 0x12922a7ce WebCore::Document::updateLayoutIgnorePendingStylesheets(WebCore::Document::RunPostLayoutTasks) 20 0x128bd982e WebCore::AccessibilityObject::updateBackingStore() 21 0x12b2461ba -[WebAccessibilityObjectWrapperBase updateObjectBackingStore] 22 0x12b255ab5 -[WebAccessibilityObjectWrapper accessibilityAttributeValue:] 23 0x10eac8709 AccessibilityController::accessibleElementById(OpaqueJSString*) 24 0x10eac7e6b getAccessibleElementByIdCallback(OpaqueJSContext const*, OpaqueJSValue*, OpaqueJSValue*, unsigned long, OpaqueJSValue const* const*, OpaqueJSValue const**) 25 0x115f43741 long long JSC::APICallbackFunction::call<JSC::JSCallbackFunction>(JSC::JSGlobalObject*, JSC::CallFrame*) 26 0x4a6f8f201027 27 0x115e45fd0 llint_entry 28 0x115e28ef3 vmEntryToJavaScript 29 0x116bf9d57 JSC::JITCode::execute(JSC::VM*, JSC::ProtoCallFrame*) 30 0x116bf93b6 JSC::Interpreter::executeProgram(JSC::SourceCode const&, JSC::JSGlobalObject*, JSC::JSObject*) 31 0x116f5ef1c JSC::evaluate(JSC::JSGlobalObject*, JSC::SourceCode const&, JSC::JSValue, WTF::NakedPtr<JSC::Exception>&)