After the landing of the initial change to move to the browser process the mixed-content checks for frame-level resources [1], this DCHECK in FirstWebContentsProfiler::DidStartNavigation [2] starts to get triggered when PlzNavigate is enabled:

  // The first navigation has to be the main frame's.
  DCHECK(navigation_handle->IsInMainFrame());

To trigger it just execute:

  cr run chrome --enable-browser-side-navigation https://www.bennish.net/mixed-content.html

Note: the same DCHECK exists in FirstWebContentsProfiler::DidFinishNavigation and its implications should also be investigated when resolving this issue.


[1] https://bugs.chromium.org/p/chromium/issues/detail?id=599495

[2] https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/metrics/first_web_contents_profiler.cc&q=%22FirstWebContentsProfiler::DidStartNavigation%22&sq=package:chromium&type=cs