This patch adds a MOZ_DIAGNOSTIC_ASSERT for assuring the OAs
are matching when the targetOrigin is "*" for the postMessage().
But it ignores the FPD in OA since the FPDs are possible to be
different.
We also add a new pref 'privacy.firstparty.isolate.block_post_message'
for allowing blocking postMessage across different FPDs.
Differential Revision: https://phabricator.services.mozilla.com/D8521
--HG--
extra : moz-landing-system : lando