Bug 1750006 - Make tests in dom/broadcastchannel/test/ dFPI compatible, r=smaug,anti-tracking-reviewers,timhuang

We are fixing mochitests that fail when network.cookie.cookieBehavior = 5, i.e. when we enable Total Cookie Protection.
This is most often due to the test assuming that an origin will always have access to its storage state when embedded as
a third party.

In this case I had to request storage access to allow an embedded iframe to use a BroadcastChannel to communicate with top-level pages of the same origin.
This was only a problem in the XOrigin case where the test html file is loaded in an embedded iframe and then can't communicate with the top-level window it created.

Differential Revision: https://phabricator.services.mozilla.com/D136604

dom/broadcastchannel/tests/test_bfcache.html

@@ -18,7 +18,12 @@
    * The page which is loaded from session history should be persisted if
    * expectedPersisted is true.
    */
+
+  SimpleTest.waitForExplicitFinish();
   var testUrl1 = "testUrl1_bfcache.html";
+
+
+  function executeTest() {
     var bc1 = new BroadcastChannel("testUrl1_bfcache");
     var bc2 = new BroadcastChannel("testUrl2_bfcache");
     bc1.onmessage = function(event) {
@@ -82,13 +87,30 @@
       window.open(testUrl1, "", "noopener");
     }
 
-  SimpleTest.waitForExplicitFinish();
 
     // If Fission is disabled, the pref is no-op.
     SpecialPowers.pushPrefEnv({set: [["fission.bfcacheInParent", true]]}, () => {
       runTest();
     });
 
+  }
+
+  if (isXOrigin) {
+    // Bug 1746646: Make mochitests work with TCP enabled (cookieBehavior = 5)
+    // Acquire storage access permission here so that the BroadcastChannel used to
+    // communicate with the opened windows works in xorigin tests. Otherwise,
+    // the iframe containing this page is isolated from first-party storage access,
+    // which isolates BroadcastChannel communication.
+    SpecialPowers.wrap(document).notifyUserGestureActivation();
+    SpecialPowers.addPermission("storageAccessAPI", true, window.location.href).then(() => {
+      SpecialPowers.wrap(document).requestStorageAccess().then(() => {
+        executeTest();
+      });
+    });
+  } else {
+    executeTest();
+  }
+
   </script>
 </body>
 </html>