nasko@ says that when navigation finishes NavigationHandle should either 1) be in an errored-out or aborted or cancelled state or 2) have an associated target RenderFrameHost.  This assertion is violated in the callstack below:

[22546:22546:0719/133042.337131:FATAL:navigation_handle_impl.cc(306)] Check
failed: state_ >= WILL_PROCESS_RESPONSE (1 vs. 6)This accessor should onl
y be called after a response has been delivered for processing.
...
#7 0x7f1c2824de87 content::WebContentsImpl::DidFinishNavigation()
- At this point navigation_handle->GetNetErrorCode() was returning net::Error::OK
- So - the expectation was that it is safe to call navigation_handle->GetRenderFrameHost()

#8 0x7f1c27f284a2 content::NavigationHandleImpl::~NavigationHandleImpl()
#9 0x7f1c27f28b69 content::NavigationHandleImpl::~NavigationHandleImpl()
#10 0x7f1c27f2ee23 content::NavigationRequest::~NavigationRequest()
#11 0x7f1c27f2ef89 content::NavigationRequest::~NavigationRequest()
#12 0x7f1c27f12c95 content::FrameTreeNode::~FrameTreeNode()
#13 0x7f1c27f1324e content::FrameTreeNode::RemoveChild()
#14 0x7f1c27f10e3a content::FrameTree::RemoveFrame()
...
#16 0x7f1c27f399d4 content::RenderFrameHostImpl::OnMessageReceived()
...
#26 0x000001db866b content::MessageLoopRunner::Run()
#27 0x000001d84ae0 content::RunTaskAndWaitForInterstitialDetach()
#28 0x000001d849ef content::WaitForInterstitialDetach()
#29 0x000001231826
safe_browsing::SafeBrowsingBlockingPageBrowserTest_SecurityStateGoBackOnSubresourceInterstitial_Test::RunTestOnMainThread()