[ios] Only update navItem url on didFinish when hosts match.

Don't update navigationItem url's in didFinish if host's don't match.

Bug: 962368
Change-Id: I92e52d435d3b137b09bf7ff9729bdc886eabb786
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1613926
Reviewed-by: Danyao Wang <danyao@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660111}