Bug 1274265 - browser_broadcastchannel.js should not expose content promises to the rest of the test, r=jhao

browser/components/contextualidentity/test/browser/browser_broadcastchannel.js

@@ -34,16 +34,17 @@ add_task(function* test() {
   let channelName = "contextualidentity-broadcastchannel";
 
   // reflect the received message on title
-  let receiveMsg = ContentTask.spawn(receiver.browser, channelName,
-      function (name) {
-        return new content.window.wrappedJSObject.Promise(resolve => {
-          content.window.bc = new content.window.BroadcastChannel(name);
-          content.window.bc.onmessage = function (e) {
-            content.document.title += e.data;
-            resolve();
-          }
-        });
+  yield ContentTask.spawn(receiver.browser, channelName,
+    function (name) {
+      content.window.testPromise = new content.window.Promise(resolve => {
+        content.window.bc = new content.window.BroadcastChannel(name);
+        content.window.bc.onmessage = function (e) {
+          content.document.title += e.data;
+          resolve();
+        }
       });
+    }
+  );
 
   let sender1 = yield* openTabInUserContext(URI, 1);
   let sender2 = yield* openTabInUserContext(URI, 2);
@@ -63,7 +64,11 @@ add_task(function* test() {
   }
 
   // make sure we have received a message
-  yield receiveMsg;
+  yield ContentTask.spawn(receiver.browser, channelName,
+    function* (name) {
+      yield content.window.testPromise.then(function() {});
+    }
+  );
 
   // Since sender1 sends before sender2, if the title is exactly
   // sender2's message, sender1's message must've been blocked