UBSan: RenderView.cpp:831:9: runtime error: load of value nnn, which is not a valid value for type 'bool' Occurs here: RenderView::RepaintRegionAccumulator::~RepaintRegionAccumulator() { if (m_wasAccumulatingRepaintRegion) // UBSan warning/ return; if (!m_rootView) return; m_rootView.get()->flushAccumulatedRepaintRegion(); } Caused by the m_wasAccumulatingRepaintRegion instance variable not being initialized: class RepaintRegionAccumulator { WTF_MAKE_NONCOPYABLE(RepaintRegionAccumulator); public: RepaintRegionAccumulator(RenderView*); ~RepaintRegionAccumulator(); private: WeakPtr<RenderView> m_rootView; bool m_wasAccumulatingRepaintRegion; // BUG: No default initialization. }; Affects the following tests: editing/inserting/insert-list-user-select-none-crash.html fast/dom/clientWidthAfterDocumentIsRemoved.html fast/scrolling/iframe-scrollable-after-back.html fast/text/crash-font-family-parsed.html html5lib/generated/run-template-write.html imported/blink/plugins/renderless-plugin-creation-doesnt-crash-without-frame.html imported/w3c/web-platform-tests/css/cssom-view/scrolling-no-browsing-context.html imported/w3c/web-platform-tests/dom/ranges/Range-mutations-appendChild.html imported/w3c/web-platform-tests/html/browsers/the-window-object/named-access-on-the-window-object/navigated-named-objects.window.html imported/w3c/web-platform-tests/html/semantics/forms/the-label-element/clicking-interactive-content.html imported/w3c/web-platform-tests/html/syntax/parsing/html5lib_template.html imported/w3c/web-platform-tests/html/syntax/parsing/template/creating-an-element-for-the-token/template-owner-document.html imported/w3c/web-platform-tests/selection/addRange-12.html imported/w3c/web-platform-tests/shadow-dom/untriaged/html-elements-in-shadow-trees/html-forms/test-001.html media/track/track-remove-crash.html svg/custom/animate-reference-crash.html