Clear stale NavigationParams from HistoryController.

      This prevents newly created iframes during a back/forward from
targeting the wrong NavigationEntry.

BUG=623319
TEST=See bug comment 20 for repro steps.
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2144823002
Cr-Commit-Position: refs/heads/master@{#404870}