Currently, the NavigateToURLFromRenderer() helper checks success by comparing URLs, but that may be fragile with error pages.  Things should still work, since an error page shouldn't change the last committed URL for the observer, which is initially empty, but we should make this more robust and explicitly check that the navigation did not result in an error page.

Filing to follow up on a comment in https://chromium-review.googlesource.com/c/chromium/src/+/1122840/1/content/browser/frame_host/render_frame_host_manager_browsertest.cc#4449