Steps to reproduce: 1) Go to https://bugs.webkit.org/attachment.cgi?id=156687&action=review 2) Resize the page smaller 3) Scroll the page ASSERTION FAILED: rootLayer == m_clipRectsCache->m_clipRectsRoot[clipRectsType] /Users/antti/webkit/OpenSource/Source/WebCore/rendering/RenderLayer.cpp(3884) : void WebCore::RenderLayer::updateClipRects(const WebCore::RenderLayer *, WebCore::RenderRegion *, WebCore::ClipRectsType, WebCore::OverlayScrollbarSizeRelevancy) 1 0x10419049c WebCore::RenderLayer::updateClipRects(WebCore::RenderLayer const*, WebCore::RenderRegion*, WebCore::ClipRectsType, WebCore::OverlayScrollbarSizeRelevancy) 2 0x104190f7d WebCore::RenderLayer::parentClipRects(WebCore::RenderLayer const*, WebCore::RenderRegion*, WebCore::ClipRectsType, WebCore::ClipRects&, WebCore::OverlayScrollbarSizeRelevancy) const 3 0x10418a1f6 WebCore::RenderLayer::backgroundClipRect(WebCore::RenderLayer const*, WebCore::RenderRegion*, WebCore::ClipRectsType, WebCore::OverlayScrollbarSizeRelevancy) const 4 0x10418b6a9 WebCore::RenderLayer::calculateRects(WebCore::RenderLayer const*, WebCore::RenderRegion*, WebCore::ClipRectsType, WebCore::FractionalLayoutRect const&, WebCore::FractionalLayoutRect&, WebCore::ClipRect&, WebCore::ClipRect&, WebCore::ClipRect&, WebCore::OverlayScrollbarSizeRelevancy) const 5 0x10419158f WebCore::RenderLayer::localClipRect() const 6 0x10417f876 WebCore::RenderLayer::calculateLayerBounds(WebCore::RenderLayer const*, WebCore::RenderLayer const*, unsigned int) 7 0x10417fddd WebCore::RenderLayer::calculateLayerBounds(WebCore::RenderLayer const*, WebCore::RenderLayer const*, unsigned int) 8 0x1041af7b9 WebCore::RenderLayerCompositor::calculateCompositedBounds(WebCore::RenderLayer const*, WebCore::RenderLayer const*) 9 0x1041a37f4 WebCore::RenderLayerBacking::updateCompositedBounds() 10 0x1041ae0a9 WebCore::RenderLayerCompositor::rebuildCompositingLayerTree(WebCore::RenderLayer*, WTF::Vector<WebCore::GraphicsLayer*, 0ul>&, int) 11 0x1041ae3bb WebCore::RenderLayerCompositor::rebuildCompositingLayerTree(WebCore::RenderLayer*, WTF::Vector<WebCore::GraphicsLayer*, 0ul>&, int) 12 0x1041ae3bb WebCore::RenderLayerCompositor::rebuildCompositingLayerTree(WebCore::RenderLayer*, WTF::Vector<WebCore::GraphicsLayer*, 0ul>&, int) 13 0x1041ad250 WebCore::RenderLayerCompositor::updateCompositingLayers(WebCore::CompositingUpdateType, WebCore::RenderLayer*) 14 0x103613e25 WebCore::FrameView::updateFixedElementsAfterScrolling() 15 0x1043b716a WebCore::ScrollView::scrollTo(WebCore::IntSize const&) 16 0x103616251 WebCore::FrameView::scrollTo(WebCore::IntSize const&) 17 0x1043b7060 WebCore::ScrollView::setScrollOffset(WebCore::IntPoint const&) 18 0x1043b709f non-virtual thunk to WebCore::ScrollView::setScrollOffset(WebCore::IntPoint const&) 19 0x104390f06 WebCore::ScrollableArea::scrollPositionChanged(WebCore::IntPoint const&) 20 0x104390e9f WebCore::ScrollableArea::notifyScrollPositionChanged(WebCore::IntPoint const&) 21 0x1043a97ea WebCore::ScrollingCoordinator::updateMainFrameScrollPositionAndScrollLayerPosition() 22 0x1043af570 WTF::FunctionWrapper<void (WebCore::ScrollingCoordinator::*)()>::operator()(WebCore::ScrollingCoordinator*) 23 0x1043af4f5 WTF::BoundFunctionImpl<WTF::FunctionWrapper<void (WebCore::ScrollingCoordinator::*)()>, void (WebCore::ScrollingCoordinator*)>::operator()() 24 0x1025990e5 WTF::Function<void ()>::operator()() const 25 0x10259715d WTF::callFunctionObject(void*) 26 0x102596c85 WTF::dispatchFunctionsFromMainThread() 27 0x102599715 -[JSWTFMainThreadCaller call] 28 0x7fff8a0968a7 __NSThreadPerformPerform 29 0x7fff8e4f9841 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ 30 0x7fff8e4f9165 __CFRunLoopDoSources0 31 0x7fff8e51c4e5 __CFRunLoopRun
This seems to have fixed itself.
Probably fixed by one of my overlay scrollbar/clip rects fixes.