Fix DidCreateNewEntry in NavigationSimulator

This CL fixes the way we compute whether the navigation resulted in a
new NavigationEntry in NavigationSimulator, fixes some unit_tests that
were relying on improper behavior and converts some content_unittests
that needed the behavior fixed to switch to using NavigationSimulator.

Bug: 728571
Change-Id: I087c0882f2f1bcc804a843b0ece1f7cc4bc36bf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1550444
Auto-Submit: Camille Lamy <clamy@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648222}