The test fails DCHECK on line 38 because WKBackForwardList is empty when CommitPendingItem() is called:
FATAL:wk_based_navigation_manager_impl.mm(38)] Check failed: wk_item. 

This is because the navigation manager used in test is not associated with a real WKWebView.

0   ios_chrome_unittests                0x000000010399022d base::debug::StackTrace::StackTrace(unsigned long) + 157
1   ios_chrome_unittests                0x000000010399026d base::debug::StackTrace::StackTrace(unsigned long) + 29
2   ios_chrome_unittests                0x000000010398ed2c base::debug::StackTrace::StackTrace() + 28
3   ios_chrome_unittests                0x00000001039ee90f logging::LogMessage::~LogMessage() + 479
4   ios_chrome_unittests                0x00000001039ec465 logging::LogMessage::~LogMessage() + 21
5   ios_chrome_unittests                0x000000010242c994 (anonymous namespace)::SetNavigationItemInWKItem(WKBackForwardListItem*, std::__1::unique_ptr<web::NavigationItemImpl, std::__1::default_delete<web::NavigationItemImpl> >) + 276
6   ios_chrome_unittests                0x000000010242d1ae web::WKBasedNavigationManagerImpl::CommitPendingItem() + 830
7   ios_chrome_unittests                0x0000000101c524e5 (anonymous namespace)::TabModelTest_AddWithLinkTransitionAndIndex_Test::TestBody() + 1157