When setting the referrer in the current history item, set the correct policy

Found this while changing chromium to use the referrer policy stored in
the request: without this ReferrerPolicyTest.History fails.

BUG=none
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/137703011

git-svn-id: svn://svn.chromium.org/blink/trunk@166272 bbb929c8-8fbe-4397-9dbb-9b2b20218538