Bug 1526332 - Enable dom.security.featurePolicy on beta and release. r=jgraham

Differential Revision: https://phabricator.services.mozilla.com/D19672

--HG--
extra : moz-landing-system : lando

testing/web-platform/meta/html/dom/interfaces.https.html.ini

@@ -1,3 +1,4 @@
+prefs: [dom.security.featurePolicy.enabled:true]
 [interfaces.https.html?include=(Document|Window)]
   [Document interface: attribute domain]
     expected: FAIL