Seen here:
https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/57961
https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/57957

[20245:20245:1011/093725:FATAL:web_contents_observer_sanity_checker.cc(357)] Check failed: render_frame_created_happened. A RenderFrameHost pointer was passed to a WebContentsObserver method, but WebContentsObserver::RenderFrameCreated was never called for that RenderFrameHost: (8, 2 -> chrome-extension://keokedhejcenifoconafdijmnobkdfid/)
#0 0x7f3a2f5c8aae base::debug::StackTrace::StackTrace()
#1 0x7f3a2f63655f logging::LogMessage::~LogMessage()
#2 0x0000038365a6 content::WebContentsObserverSanityChecker::AssertRenderFrameExists()
#3 0x000003836b1b content::WebContentsObserverSanityChecker::RenderFrameHostChanged()
#4 0x7f3a282c3c46 content::WebContentsImpl::NotifyFrameSwapped()
#5 0x7f3a282c7fcd content::WebContentsImpl::NotifySwappedFromRenderManager()
#6 0x7f3a27a3fa26 content::RenderFrameHostManager::Init()
#7 0x7f3a279afc4b content::FrameTreeNode::AddChild()
#8 0x7f3a279a8c11 content::FrameTree::AddFrame()
#9 0x7f3a27a0b583 content::RenderFrameHostImpl::OnCreateChildFrame()
#10 0x7f3a27a57e82 content::(anonymous namespace)::CreateChildFrameOnUI()
...

Is this related to bug 620194?