I have tried very hard to change the ordering when fixing webNavigation extension API to work with PlzNavigate. However, it turns out it is not simple at all and is fraught with peril. I resorted to handling this case explicitly in the webNavigation code internally.

I would suggest if possible to actually account for this case within the page load metrics code. Let me know if I can be of help.

Bryan, PLM code is currently using NavigationThrottle::WillStartRequest instead of WebContentsObserver::DidStartNavigation. And I see the comment in metrics_navigation_throttle.h that "Data from the NavigationHandle accessed at this point is used to obtain more reliable abort metrics (like page transition type)." Why is that more reliable?

Good question - some of the properties of NavigationHandle that we care about, such as HasUserGesture IIRC, are not available in DidStartNavigation, but are available in WillStartRequest. The reason for this seems to be historical & some of these getters could be made available at construction time, but it requires refactoring. I did try to refactor nav handle and related code a bit to fix this for user gesture tracking, but my change regressed an android test that wasn't part of the CQ so I had to revert it & I decided to table the work so never re-landed.

Ideally all of the properties we care about would be available in DidStartNavigation but that's not currently the case, so we hook WillStartRequest instead.

You can get a sense for which properties are available at which times by looking at the state_-related DCHECKs in the getters in navigation_handle_impl.cc, for example:

bool NavigationHandleImpl::HasUserGesture() {
  CHECK_NE(INITIAL, state_)
      << "This accessor should not be called before the request is started.";
  return has_user_gesture_;
}

PageTransition is another example of a property not available until WillStartRequest.

Note too that some of these properties can be 'updated' at commit time, for reasons that weren't always totally clear. It's probably best to trace how each navhandle property you are interested in is updated to understand its unique constraints / properties.