Bug 1618447, gShouldObserveSubframes should only be set for the out of process frames part of the test, r=kmag

Differential Revision: https://phabricator.services.mozilla.com/D64864

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

browser/base/content/test/webrtc/browser_devices_get_user_media_in_frame.js

@@ -9,9 +9,7 @@ SpecialPowers.pushPrefEnv({
   ],
 });
 
-// When the frames are in different processes, add observers to each frame,
-// to ensure that the notifications don't get sent in the wrong process.
-const gShouldObserveSubframes = SpecialPowers.useRemoteSubframes;
+let gShouldObserveSubframes = false;
 
 var gTests = [
   {
@@ -582,6 +580,10 @@ add_task(async function test_inprocess() {
 });
 
 add_task(async function test_outofprocess() {
+  // When the frames are in different processes, add observers to each frame,
+  // to ensure that the notifications don't get sent in the wrong process.
+  gShouldObserveSubframes = SpecialPowers.useRemoteSubframes;
+
   let observeSubFrameIds = gShouldObserveSubframes ? ["frame1", "frame2"] : [];
   await runTests(gTests, {
     relativeURI: "get_user_media_in_oop_frame.html",