Description: imported/w3c/web-platform-tests/css/css-align/baseline-rules/synthesized-baseline-flexbox-001.html After consistently passing the first instance of a flaky crash was at 253855@main. Then at 253866@main there was a fix and the test consistently passed again until at 253946@main where it began to flaky crash again. REPRODUCTION STEPS I can reproduce this on 253946@main but cannot reproduce it on 253945@main or earlier. Command: run-webkit-tests --debug -1 --exit-after-n-crashes-or-timeouts 1 -f --no-retry --child-processes 1 --test-list <test-list attached> Result: Regressions: Unexpected crashes (1) media/modern-media-controls/pip-support/pip-support-click.html [ Crash ] History: https://results.webkit.org/?suite=layout-tests&test=imported%2Fw3c%2Fweb-platform-tests%2Fcss%2Fcss-align%2Fbaseline-rules%2Fsynthesized-baseline-flexbox-001.html&platform=mac&flavor=wk1&style=debug Crash Log: No crash log found for DumpRenderTree:38254. stdout: PASS .wrapper 1 PASS .wrapper 2 PASS .wrapper 3 PASS .wrapper 4 PASS .wrapper 5 PASS .wrapper 6 PASS .wrapper 7 stderr: ASSERTION FAILED: !needsSlowPutIndexing() runtime/JSObject.cpp(1794) : JSC::ArrayStorage *JSC::JSObject::ensureArrayStorageSlow(JSC::VM &) 1 0x1029f4610 WTFCrash 2 0x103030bf0 JSC::AbstractSlotVisitor::ReferrerToken::ReferrerToken(JSC::HeapCell*) 3 0x1047c57c4 JSC::JSObject::ensureArrayStorageSlow(JSC::VM&) 4 0x1047cb434 JSC::JSObject::enterDictionaryIndexingMode(JSC::VM&) 5 0x1047ce954 JSC::JSObject::switchToSlowPutArrayStorage(JSC::VM&) 6 0x1047174c0 JSC::JSGlobalObject::haveABadTime(JSC::VM&) 7 0x1047cec48 JSC::JSObject::setPrototypeDirect(JSC::VM&, JSC::JSValue) 8 0x1047fc164 JSC::JSProxy::setTarget(JSC::VM&, JSC::JSGlobalObject*) 9 0x12e08cae8 WebCore::JSWindowProxy::setWindow(JSC::VM&, WebCore::JSDOMGlobalObject&) 10 0x12e08c7c4 WebCore::JSWindowProxy::setWindow(WebCore::AbstractDOMWindow&) 11 0x12e0b2f7c WebCore::WindowProxy::setDOMWindow(WebCore::AbstractDOMWindow*) 12 0x12f5fdc34 WebCore::FrameLoader::clear(WTF::RefPtr<WebCore::Document, WTF::RawPtrTraits<WebCore::Document>, WTF::DefaultRefDerefTraits<WebCore::Document> >&&, bool, bool, bool, WTF::Function<void ()>&&) 13 0x12f57f3b4 WebCore::DocumentWriter::begin(WTF::URL const&, bool, WebCore::Document*, WebCore::ProcessQualified<WTF::UUID>) 14 0x12f578d00 WebCore::DocumentLoader::commitData(WebCore::SharedBuffer const&) 15 0x12f5787a0 WebCore::DocumentLoader::finishedLoading() 16 0x12f5842ac WebCore::DocumentLoader::maybeLoadEmpty() 17 0x12f5844f0 WebCore::DocumentLoader::startLoadingMainResource() 18 0x12f63425c WebCore::FrameLoader::continueLoadAfterNavigationPolicy(WebCore::ResourceRequest const&, WebCore::FormState*, WebCore::NavigationPolicyDecision, WebCore::AllowNavigationToInvalidURL)::$_11::operator()() 19 0x12f633df4 WTF::Detail::CallableWrapper<WebCore::FrameLoader::continueLoadAfterNavigationPolicy(WebCore::ResourceRequest const&, WebCore::FormState*, WebCore::NavigationPolicyDecision, WebCore::AllowNavigationToInvalidURL)::$_11, void>::call() 20 0x12aff7a9c WTF::Function<void ()>::operator()() const 21 0x12b05911c WTF::CompletionHandler<void ()>::operator()() 22 0x12f607d6c WebCore::FrameLoader::continueLoadAfterNavigationPolicy(WebCore::ResourceRequest const&, WebCore::FormState*, WebCore::NavigationPolicyDecision, WebCore::AllowNavigationToInvalidURL) 23 0x12f630264 WebCore::FrameLoader::loadWithDocumentLoader(WebCore::DocumentLoader*, WebCore::FrameLoadType, WTF::RefPtr<WebCore::FormState, WTF::RawPtrTraits<WebCore::FormState>, WTF::DefaultRefDerefTraits<WebCore::FormState> >&&, WebCore::AllowNavigationToInvalidURL, WTF::CompletionHandler<void ()>&&)::$_8::operator()(WebCore::ResourceRequest const&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision) 24 0x12f630104 WTF::Detail::CallableWrapper<WebCore::FrameLoader::loadWithDocumentLoader(WebCore::DocumentLoader*, WebCore::FrameLoadType, WTF::RefPtr<WebCore::FormState, WTF::RawPtrTraits<WebCore::FormState>, WTF::DefaultRefDerefTraits<WebCore::FormState> >&&, WebCore::AllowNavigationToInvalidURL, WTF::CompletionHandler<void ()>&&)::$_8, void, WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision>::call(WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision) 25 0x12f686b98 WTF::Function<void (WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision)>::operator()(WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision) const 26 0x12f664ac4 WTF::CompletionHandler<void (WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision)>::operator()(WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision) 27 0x12f6638f0 WebCore::FrameLoader::PolicyChecker::checkNavigationPolicy(WebCore::ResourceRequest&&, WebCore::ResourceResponse const&, WebCore::DocumentLoader*, WTF::RefPtr<WebCore::FormState, WTF::RawPtrTraits<WebCore::FormState>, WTF::DefaultRefDerefTraits<WebCore::FormState> >&&, WTF::CompletionHandler<void (WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormState, WTF::EmptyCounter>&&, WebCore::NavigationPolicyDecision)>&&, WebCore::PolicyDecisionMode) 28 0x12f606f3c WebCore::FrameLoader::loadWithDocumentLoader(WebCore::DocumentLoader*, WebCore::FrameLoadType, WTF::RefPtr<WebCore::FormState, WTF::RawPtrTraits<WebCore::FormState>, WTF::DefaultRefDerefTraits<WebCore::FormState> >&&, WebCore::AllowNavigationToInvalidURL, WTF::CompletionHandler<void ()>&&) 29 0x12f601fdc WebCore::FrameLoader::load(WebCore::DocumentLoader&) 30 0x12f605cc8 WebCore::FrameLoader::load(WebCore::FrameLoadRequest&&) 31 0x14c7d4414 -[WebFrame loadRequest:]