[Nav Experiment] Update incorrect DCHECK assumption in didFailNavigation

This DCHECK is meant to assert that placeholder navigation never fails.
However, webView.URL may have reverted to the previous entry when a
failure happens so is not always the URL that triggers the error. The
correct approach is to check the error URL.

Bug: 864525
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I4efb01041a39f87c4c1ac36115c93364bd41aff9
Reviewed-on: https://chromium-review.googlesource.com/1151391
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578359}
1 file changed