This test fails the assumption that WKBackForwardList.currentItem is not nil in WKNavigationDelegate's |-webView:didCommitNavigation| callback. It uses WebTestWebState::LoadHTML(), which calls WKWebView's |-loadHTMLString:baseURL|, which does not generate a WKBackForwardListItem.

This is a flaw in our assumption about how WKWebView navigation works.

A workaround is to load about:blank into the web view as part of test setup. But finding a better solution can simplify WebUI handling as well.

Callstack:
FATAL:wk_based_navigation_manager_impl.mm(38)] Check failed: wk_item.
0   ios_web_unittests                   0x0000000100e8282d base::debug::StackTrace::StackTrace(unsigned long) + 157
1   ios_web_unittests                   0x0000000100e8286d base::debug::StackTrace::StackTrace(unsigned long) + 29
2   ios_web_unittests                   0x0000000100e80d8c base::debug::StackTrace::StackTrace() + 28
3   ios_web_unittests                   0x0000000100edb91f logging::LogMessage::~LogMessage() + 479
4   ios_web_unittests                   0x0000000100ed9475 logging::LogMessage::~LogMessage() + 21
5   ios_web_unittests                   0x0000000100a02cc4 (anonymous namespace)::SetNavigationItemInWKItem(WKBackForwardListItem*, std::__1::unique_ptr<web::NavigationItemImpl, std::__1::default_delete<web::NavigationItemImpl> >) + 276
6   ios_web_unittests                   0x0000000100a034de web::WKBasedNavigationManagerImpl::CommitPendingItem() + 830
7   ios_web_unittests                   0x0000000100a838a4 -[CRWWebController didStartLoadingURL:] + 196
8   ios_web_unittests                   0x0000000100a8368d -[CRWWebController webPageChanged] + 621
9   ios_web_unittests                   0x0000000100a9a77d -[CRWWebController webView:didCommitNavigation:] + 3453
10  WebKit                              0x0000000108822509 WebKit::NavigationState::NavigationClient::didCommitNavigation(WebKit::WebPageProxy&, API::Navigation*, API::Object*) + 91