Debugging some more, the problem seems to be that the call to goBack on line 62 isn't actually going back, so there's nothing to go forward to in the call to goForward.

In the call to goBack, we start with WKCurrentItemIndex 1 and pending_item_index_ -1, and we call goToIndex(0). That leads to FinishGoToIndex(0), which calls goToBackForwardListItem on WKWebView. But after that call, WKCurrentItemIndex is still 1.

Is the expected behavior of goToBackForardListItem that it changes WKCurrentItemIndex synchronously? If so, the bug is that it isn't changing, and otherwise the bug is that the test is expecting it to change right away.

And trying to understand the test some more, it does wait for loading to become false on the WKWebView after calling goBack, but it's false immediately.

Thanks for debugging! I don't think goToBackForwardListItem changes WKCurrentItemIndex synchronously because it's sending an IPC to the WebCore process.

Correcting what I said in Comment 2, the test is waiting for loading to become false CWVWebView, not on WKWebView. It's false on CWVWebView, but isLoading is *true* on WKWebView. So CWVWebView's webStateDidStartLoading method might not be getting called as expected.

webStateDidStartLoading would normally (in the legacy code path) get called during WebStateImpl::LoadCurrentItem which happens in LegacyNavigationManagerImpl::FinishGoToIndex (see the full call stack below). But WKBasedNavigationManagerImpl::FinishGoToIndex skips this logic by navigating using WKWebView's goToBackForwardListItem.

One approach to deal with this would be to do KVO on WKWebView's isLoading to keep CWVWebView's loading up-to-date, but KVO on isLoading is explicitly turned off for the new navigation manager here: 
https://cs.chromium.org/chromium/src/ios/web/web_state/ui/crw_web_controller.mm?rcl=737ab6731d14c91ffb665e837425c8ec98c7be10&l=1044

Another approach would be to directly expose WKWebView's isLoading and have the test wait on that when the new navigation manager is enabled.

Here's the call stack for webStateDidStartLoading get called by the old navigation manager:
  * frame #0: 0x0000000114d62684 ChromeWebView`::-[CWVWebView webStateDidStartLoading:](self=0x00007fb399e0ab70, _cmd="webStateDidStartLoading:", webState=0x00007fb399d3ffc0) at cwv_web_view.mm:264
    frame #1: 0x0000000114d05afb ChromeWebView`web::WebStateObserverBridge::DidStartLoading(this=0x000060000003d2e0) at web_state_observer_bridge.mm:67
    frame #2: 0x0000000114ceef6a ChromeWebView`web::WebStateImpl::SetIsLoading(this=0x00007fb399d3ffc0, is_loading=true) at web_state_impl.mm:225
    frame #3: 0x0000000114c895e4 ChromeWebView`::-[CRWWebController registerLoadRequestForURL:referrer:transition:sameDocumentNavigation:](self=0x00007fb399e08120, _cmd="registerLoadRequestForURL:referrer:transition:sameDocumentNavigation:", requestURL=0x00007fff500d0540, referrer=0x00007fff500d07b8, transition=16777217, sameDocumentNavigation=NO) at crw_web_controller.mm:1476
    frame #4: 0x0000000114cba960 ChromeWebView`::__55-[CRWWebController loadRequestForCurrentNavigationItem]_block_invoke.1137(.block_descriptor=<unavailable>) at crw_web_controller.mm:5178
    frame #5: 0x0000000114cb9977 ChromeWebView`::-[CRWWebController loadRequestForCurrentNavigationItem](self=0x00007fb399e08120, _cmd="loadRequestForCurrentNavigationItem") at crw_web_controller.mm:5203
    frame #6: 0x0000000114c8af2a ChromeWebView`::-[CRWWebController loadCurrentURLInWebView](self=0x00007fb399e08120, _cmd="loadCurrentURLInWebView") at crw_web_controller.mm:1619
    frame #7: 0x0000000114c8e04f ChromeWebView`::-[CRWWebController loadCurrentURL](self=0x00007fb399e08120, _cmd="loadCurrentURL") at crw_web_controller.mm:1868
    frame #8: 0x0000000114cf6bde ChromeWebView`web::WebStateImpl::LoadCurrentItem(this=0x00007fb399d3ffc0) at web_state_impl.mm:775
    frame #9: 0x0000000114bf83bd ChromeWebView`web::LegacyNavigationManagerImpl::FinishGoToIndex(this=0x0000600000272a00, index=0) at legacy_navigation_manager_impl.mm:320
    frame #10: 0x0000000114c017b9 ChromeWebView`web::NavigationManagerImpl::GoToIndex(this=0x0000600000272a00, index=0) at navigation_manager_impl.mm:191
    frame #11: 0x0000000114bf6c10 ChromeWebView`web::LegacyNavigationManagerImpl::GoBack(this=0x0000600000272a00) at legacy_navigation_manager_impl.mm:200
    frame #12: 0x0000000114d614fa ChromeWebView`::-[CWVWebView goBack](self=0x00007fb399e0ab70, _cmd="goBack") at cwv_web_view.mm:162

 Issue 775069  has been merged into this issue.

 Issue 775076  has been merged into this issue.

Actually, this is a duplicate of  crbug.com/776373 .
Verified that this test now passes after crrev.com/c/762176.

Actually, this is a duplicate of  crbug.com/776373 .
Verified that this test now passes after crrev.com/c/762176.