This is a testharness.js-based test.
PASS postMessaging to a same-origin iframe via MessageChannel allows them to see each others' modifications
PASS postMessaging to a same-site iframe via MessageChannel should fail
PASS postMessaging to a cross-site iframe via MessageChannel should fail
FAIL postMessaging with a MessageChannel that's been cross-site should succeed assert_true: expected true got false
Harness: the test ran to completion.