Don't compare security origins by pointers but by contents

Due to this, we didn't set the referrer header correctly under certain
circumstances.

BUG=327440
R=abarth@chromium.org,japhet@chromium.org
TEST=security/tests/referrer-on-client-redirect.html

Review URL: https://codereview.chromium.org/112703002

git-svn-id: svn://svn.chromium.org/blink/trunk@163719 bbb929c8-8fbe-4397-9dbb-9b2b20218538