Created attachment 321601 [details] Crash Log The test imported/w3c/web-platform-tests/custom-elements/microtasks-and-constructors.html was seen crashing with the assertion failure: ASSERTION FAILED: callback /Volumes/Data/slave/sierra-debug/build/Source/WebCore/bindings/js/JSCallbackData.cpp(44) : static JSC::JSValue WebCore::JSCallbackData::invokeCallback(WebCore::JSDOMGlobalObject &, JSC::JSObject *, JSC::JSValue, JSC::MarkedArgumentBuffer &, WebCore::JSCallbackData::CallbackType, JSC::PropertyName, NakedPtr<JSC::Exception> &) 1 0x106d7782d WTFCrash 2 0x114a7190a WebCore::JSCallbackData::invokeCallback(WebCore::JSDOMGlobalObject&, JSC::JSObject*, JSC::JSValue, JSC::MarkedArgumentBuffer&, WebCore::JSCallbackData::CallbackType, JSC::PropertyName, WTF::NakedPtr<JSC::Exception>&) 3 0x115080fd2 WebCore::JSCallbackDataWeak::invokeCallback(JSC::JSValue, JSC::MarkedArgumentBuffer&, WebCore::JSCallbackData::CallbackType, JSC::PropertyName, WTF::NakedPtr<JSC::Exception>&) 4 0x115080d96 WebCore::JSMutationCallback::handleEvent(WebCore::MutationObserver&, WTF::Vector<WTF::Ref<WebCore::MutationRecord>, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc> const&, WebCore::MutationObserver&) 5 0x115937a38 WebCore::MutationObserver::deliver() 6 0x115937fc6 WebCore::MutationObserver::notifyMutationObservers() 7 0x11593a221 WebCore::MutationObserverMicrotask::run() 8 0x11590410d WebCore::MicrotaskQueue::performMicrotaskCheckpoint() 9 0x11500e3c9 WebCore::JSMainThreadExecState::didLeaveScriptContext(JSC::ExecState*) 10 0x114a7242e WebCore::JSMainThreadExecState::~JSMainThreadExecState() 11 0x114a72285 WebCore::JSMainThreadExecState::~JSMainThreadExecState() 12 0x115f52e98 WebCore::JSMainThreadExecState::profiledEvaluate(JSC::ExecState*, JSC::ProfilingReason, JSC::SourceCode const&, JSC::JSValue, WTF::NakedPtr<JSC::Exception>&) 13 0x115f52c78 WebCore::ScriptController::evaluateInWorld(WebCore::ScriptSourceCode const&, WebCore::DOMWrapperWorld&, WebCore::ExceptionDetails*) 14 0x115f52f6d WebCore::ScriptController::evaluate(WebCore::ScriptSourceCode const&, WebCore::ExceptionDetails*) 15 0x115f68682 WebCore::ScriptElement::executeClassicScript(WebCore::ScriptSourceCode const&) 16 0x115f66c8f WebCore::ScriptElement::prepareScript(WTF::TextPosition const&, WebCore::ScriptElement::LegacyTypeSupport) 17 0x11466abc0 WebCore::HTMLScriptRunner::runScript(WebCore::ScriptElement&, WTF::TextPosition const&) 18 0x11466aa2f WebCore::HTMLScriptRunner::execute(WTF::Ref<WebCore::ScriptElement>&&, WTF::TextPosition const&) 19 0x11457ff12 WebCore::HTMLDocumentParser::runScriptsForPausedTreeBuilder() 20 0x114580473 WebCore::HTMLDocumentParser::pumpTokenizerLoop(WebCore::HTMLDocumentParser::SynchronousMode, bool, WebCore::PumpSession&) 21 0x11457f108 WebCore::HTMLDocumentParser::pumpTokenizer(WebCore::HTMLDocumentParser::SynchronousMode) 22 0x11457ec5b WebCore::HTMLDocumentParser::pumpTokenizerIfPossible(WebCore::HTMLDocumentParser::SynchronousMode) 23 0x114581e89 WebCore::HTMLDocumentParser::resumeParsingAfterScriptExecution() 24 0x11458228e WebCore::HTMLDocumentParser::notifyFinished(WebCore::PendingScript&) 25 0x1145822ec non-virtual thunk to WebCore::HTMLDocumentParser::notifyFinished(WebCore::PendingScript&) 26 0x115a4c8e7 WebCore::PendingScript::notifyClientFinished() 27 0x115a4c949 WebCore::PendingScript::notifyFinished(WebCore::LoadableScript&) 28 0x115716839 WebCore::LoadableScript::notifyClientFinished() 29 0x115713930 WebCore::LoadableClassicScript::notifyFinished(WebCore::CachedResource&) 30 0x115713a5c non-virtual thunk to WebCore::LoadableClassicScript::notifyFinished(WebCore::CachedResource&) 31 0x113abf29d WebCore::CachedResource::checkNotify() First crash was with https://build.webkit.org/builders/Apple%20El%20Capitan%20Debug%20WK2%20(Tests)/builds/2906
<rdar://problem/34605960>