Do not use NavigationEntry to block history navigations.

This is no longer necessary after r477371.

BUG=777419
TEST=See bug for repro steps.
TBR=creis@chromium.org

(cherry picked from commit 56a84aa67bb071a33a48ac1481b555c48e0a9a59)

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: I701e4d4853858281b43e3743b12274dbeadfbf18
Reviewed-on: https://chromium-review.googlesource.com/733959
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Charlie Reis <creis@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#511942}
Reviewed-on: https://chromium-review.googlesource.com/751765
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/branch-heads/3239@{#355}
Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
8 files changed