Update HistoryController::current_entry_ on all main frame back/forwards.

      This fixes a case where it was left stale on a cross-origin commit
because the provisional_entry_ had been cleared by a different commit.

BUG=623319
TEST=See bug comment 14 for repro steps.
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2134493002
Cr-Commit-Position: refs/heads/master@{#404537}